The best place to start is with the Code of Canon Law. It will lay out what the legal requirements for marriage in the Church are.
It can, and usually does, get very complicated.
For example, my husband & I, both confirmed catholics, were not married in the church (the reasons do not matter for this discussion, and that fact has been remidied), but also lacked the “dispensation” for not being married in the Church, so even though the state considered us married, the Church, in fact, did not.
Much of our issue was that we were not told of certain requirements, and actually had our rights under canon law violated not by one, but by 2 priests at 2 different parishes.
So start with Canon Law, then if there are questions after that, the best person to talk with would be a priest or deacon.