The Short answer is... 1. Attend Mass at a Catholic church. 2. Speak with a priest or deacon about becoming Catholic. 3. Attend the group Rite of Christian Initiation for Adults group or Journey in Faith classes. 4. Complete the session with a sponsor. 5. Get baptized (received), confirmed, and receive the Eucharist
The Longer and more full answer is given on WikiHow:
Sit down with yourself for a serious talk. Becoming a Catholic will change the rest of your life. It's not like deciding to be a hipster or marking "Y" on your driver's license to be an organ donor. This will become a part of you and it's not something you want to do half-heartedly. Sure, there are shiny lights at Christmastime, but those can't be the basis for your faith (pretty though they are).
Are you familiar enough with the teachings of the Catholic Church to be able to say that you know this is something you want to be a part of? If the answer is yes, great! Keep on reading. If you're not so sure, seek out a friend or a member of the clergy for information. And there's always the Internet!
Do you believe that Jesus is the Son of God and the true Messiah? Do you have faith in the Holy Trinity -- the Father, the Son, and the Holy Spirit? How about the Virgin Mary and transubstantiation? Yes? Great! Moving on.
Read the Bible and the Catechism. The Catechism (you probably know what the Bible is, huh?) is basically a set of instructions for Christians in the form of questions and answers. It may be just the source you need to seal the deal!
If time isn't on your side, read Genesis and the Gospels. You'll get a good grasp on the creation story and the story of Jesus. What's more, when you do talk to a priest and express your interest, it'll be clear you've done your homework
Know your circumstances. If you have no prior history with the Catholic church, you'll be going through the process outlined in this article -- namely, RCIA or JIF (Rite of Christian Initiation for Adults, Journey in Faith) classes and getting the full head-to-toe spa treatment at next year's Easter Vigil (Baptism, Confirmation, etc.). However, if you've been baptized but nothing else or have other previous ties to the Church, your process may be a bit different.
If you've been baptized, but your initiation process stops there, you may not need to take RCIA classes. It all depends on your education and desires. Most baptized people will go through a much shorter period of inquiry and reflection and can join the church on any Sunday.[
Visit local Catholic churches. It's not too hard -- just look under the yellow pages of the phone book under "Churches" or wander around your neighborhood. They'll be the big, pretty buildings with crosses on top, hint hint. Alternatively, search on the internet for churches and their Mass times. There is also an app for that - MassTimes is free and uses your GPS to show you what Roman Catholic Churches are in your immediate area.
Sure, finding one is good, but finding 4 is great. Think about churches the way you would think about college. They'll all offer you an education, but each one will be very different from every other. One church may turn you off while another feels like home. If you haven't found one that speaks to you, keep looking.
Attend Mass. You wouldn't buy a car without test driving it, would you? Going to church is not a privilege reserved for those in the elite Catholic club, so attend! Anyone is welcome and no questions will be asked if you do choose to go. Go with a Catholic friend who can explain when to do things and what they mean. While you won't participate in Communion, you will participate in everything else. And no, no one will notice (or care) that you didn't go up to receive the Eucharist! The church is welcoming of all.
Don't let a particular Mass or church influence your decision. Most churches have a fair amount of variation in services. Many churches often offer "teen Masses" or "guitar Masses" as well as Masses in different languages corresponding to the local minority community. Additionally, your enjoyment of the sermon may depend on the priest who is celebrating that particular Mass. So search around! There are plenty of options out there.
Pray. Just because you're not a seasoned veteran of the Catholic Church doesn't mean you can't pray. And it definitely doesn't mean God can't hear you! Take some time out of your day to pray and see how it feels. If it relaxes you or connects you to a deeper level, that's a good sign.
You're not necessarily looking for answers when you pray. Just a little talk with someone up there (saints included!) to show your appreciation, ask for help, or just to relax with and take in the moment. It can be done anywhere, anytime, anyplace, and through thought, words, singing, or action.
Contact the Parish Office of your chosen church. Inform them of your desire to convert and you're on your way! There are group classes, called RCIA (Rite of Christian Initiation for Adults), for all people wishing to convert within a period, giving you a social framework for assimilating the experience. But before you start, you'll have to go through the "precatechumenate" process -- which basically means talking to a priest, reflection and attending Mass regularly. It's not nearly as intimidating as it sounds!
Sometimes churches work like schools in that you're only allowed to go to the one designated by your geographical area. If you find one that is further away and this is the rule in your diocese, just get a letter from your local parish allowing you to attend your desired church.
Talk to a priest or deacon. He will ask you why you wish to become Catholic and in general, talk to you to be sure you are sincere in your desire and are aware of the conditions of being Catholic. If you both are ready to move forward, you will begin in the RCIA.
During a Mass, you (and everyone else in your "term") will publicly announce your intentions through the Rite of Acceptance into the Order of Catechumens and the Rite of Welcoming. Don't worry -- there's no public speaking involved. You are no longer in the pre-catechumenate process and have stepped forward to being a catechumen!
Start your Catholic education classes (RCIA). You will learn the history of the Church, the beliefs and values of the Catholic Church, and the proper order of celebration of Mass..
However, you'll be involved in many other ways! You will participate in prayers, and become involved with the community at large. Not to mention, your class will become closer and closer and do things on their own time.
Complete the season with a sponsor. Most RCIA classes take place over the course of one liturgical cycle. That way, you get to experience all the feasts, fastings, and holy days. In this time, you'll choose a sponsor - They're just there to help, answering all the questions you may have.
During this time, you may be asked to clarify your marriage status. If you are divorced but have not received an annulment, you will need to obtain one before becoming Catholic. If you are married but not by the eyes of the Catholic Church, you may be asked to get "remarried," (or have your marriage "blessed").
Begin the period of purification and enlightenment. Once the end of the liturgical cycle nears, you will be deemed "an elect." This is the part where you'll prepare for three public celebrations: the Rite of Election, the Call to Continuing Conversion, and the deal-cincher at the Easter Vigil.
The first two listed are at the beginning of Lent. When the 40 days are up, at the Easter Vigil you will be baptized, confirmed, and receive Eucharist.
Become a full-fledged Catholic. After the Easter Vigil (a truly memorable, beautiful experience), you are now a proud, valued member of the Catholic church. All your hard work and studying has paid off and you're good to go. Welcome!
In case you're curious, for the Sacraments, no, you don't really have to do anything. Showing up with a smile on your face and good intentions in your heart is really all that's required. There's no memorizing, no actions, and no final test. The church is just glad you're here. The priest will take care of the work!
Begin the period of mystagogy. Sounds magical, doesn't it? Technically, it's a lifelong process of becoming closer to God and delving deep into your Catholic beliefs. Non-technically, it ends around Pentecost and is a fancy term for exploring your experience through catechesis.
Some churches may continue to "teach" you (more like guidance when needed) for up to a year. You're still considered a newbie and may ask all the questions you need! Really, they're just there to help. Then it's out of mother's nest and into the heavens!
Journey in Faith 2017-2018 begins on THURSDAY 5th October 2017 and continues until the Easter Vigil on Saturday 31 March 2018. Pick up a leaflet in Church or speak to one of the priests.