What are the steps to become Confirmed in the Catholic church?

My original answer (below the line) no longer addresses the question, as the OP has clarified to be about a person raised Catholic who is not confirmed.

I will answer for the LA Archdiocese in the USA. I expect (but am not certain) that it is similar throughout the USA. I know it differs in other parts of the world.

Teenagers are typically confirmed during the Easter season of their 10th grade year. It is the culmination of a 2 academic year process, started during their 9th grade year. There are lots of curricula for the Confirmation process. It is done at the parish level, even for students of Catholic high schools.

The first year is typically basic faith formation, finding a sponsor, filling in the education and information gaps, getting the preparatory paperwork done, and building the cohesion of the group. It is generally pretty easy, and many kids consider it a waste of time. The second year is about Confirmation itself, the ethical and moral obligations of adult Catholics, discernment, and applying Catholic principles to life in the secular world, and personal preparation for the sacrament itself. It is challenging, and often personally difficult.

For baptized adults who received the Eucharist but were never confirmed, most parishes have an "Adult Confirmation" process, which may be similar to the "RCIA" process (see below) or may be different. The parish priests have wide latitude with respect to adults. The only real answer is to talk to the priest.

I am answering here about an unbaptized adult convert, or a baptized adult who has not received the Eucharist and seeks to join the Church. Those who are baptized and have received the Eucharist but are not confirmed should see their pastor, the process and the conditions can vary widely.

Generally speaking, the requirements for Confirmation are honest belief in the Catholic faith, a free choice to be confirmed, a period of education and discernment, and that the person is not otherwise prohibited from participating in the Eucharist. Marriage problems are the biggest impediment to the last item. I have no citation for this; it is a recollection from my training as a Confirmation Catechist.

Beyond that, the local bishops have wide latitude, particularly for converts and non-typical situations. Different dioceses give standard confirmation at different ages, have different requirements for preparation, and have different programs for initiation outside of the standard process.

The RCIA (Rite of Christian Initiation of Adults) process, of which I am a "graduate", is outlined by the Vatican but the specifics vary between dioceses and sometimes even between parishes within a diocese. The Wikipedia article has a good description of the process.

In the parish where I was confirmed, there was a single program for baptized and unbaptized, it started in September, we were confirmed at the Easter Vigil, and the program continued until Pentecost. We went to Mass on Sunday, stayed until the Profession of Faith (right after the homily), and left together (with some fanfare and a blessing from the Priest) to have class.

Note: Baptism, Eucharist and Confirmation are the "Sacraments of Initiation", and one is not "fully initiated" into the Church until one is confirmed. However, Confirmation is not required for adult membership in the Church, for reception of the Eucharist, or for marriage in the Church. It is, however, strongly encouraged, and is usually a requirement for participation in a lay ministry with the Church, to be a godparent at a Baptism, to sponsor Confirmation for someone else, or to formally witness a Marriage in the Church. Again the local bishops and pastors do have discretion.

• See Canon Law starting at Canon 879 for the specifics of Confirmation.
• See Canon Law starting at Canon 1065 for how Confirmation relates to Marriage.