From a reader…
I was baptized Greek Orthodox but left the church for 10 years. I so want to return. Can I just start going again?
This is unclear. Do you mean that you want to return to the Greek Orthodox Church? If so, ask a Greek Orthodox priest.
However, I’ll assume that you want to enter the Catholic Church and be in union with Peter, as Christ intended.
The first thing you should do is make an appointment to chat with a good and holy priest in your area. If you can get your hands on a copy of your baptismal certificate, bring that along. Some sort of proof of your baptism will be needed eventually. If you were baptized Greek Orthodox, you were most likely also confirmed (chrismated) and made your First Holy Communion.
To become Catholic, there would be no need to repeat these sacraments.
Father would simply need to see that you receive sufficient catechesis, that you know and understand what the Catholic Church teaches. He may instruct you himself, or he may entrust your instruction to someone else. As a fully initiated Christian, you shouldn’t have to go through the RCIA process (which is for the unbaptized who wish to become baptized Catholics) but there may be a series of classes or sessions that might be helpful to you.
Once Father is convinced that you are ready, he should have you make a good confession. Then he will have you make a public profession of the Catholic Faith. He will then record all of this in the parish records, with the appropriate notations concerning your confirmation and recording your marital status.
You will, I think, be received into the Catholic Church as a member of the Hellenic Greek Catholic Church, which is one of the Eastern Catholic Churches. They do not have a hierarchy or parishes in these USA… I assume you are these USA. If you wish to participate in a liturgy more akin to what you grew up with, in the Greek Orthodox Church, you may want to look into, for example, a Ruthenian Catholic parish nearby or any other Catholic parish that utilizes the Byzantine (Constantinopolitan) liturgical books. The Byzantine Catholic Church in America is in full union with Rome.