I was baptised as a baby, but didn't go to church for a long while and eventually started up again and was confirmed in my twenties. For me, that was about having developed my own belief in God and Christ, not about doing it because it was what I was brought up in. If you get baptised or confirmed as an adult, most churches will have regular meetings for a while beforehand to help you think about what you believe and what you are choosing - you could always ask at your local church about what they do and go along - if you don't then think it's for you then there won't be any pressure, but you'll maybe be clearer about it all.
If you do get baptised, you'll have to "agree" to some things about your beliefs - I've put the words to the new Church of England baptism here, but I expect the Roman Catholic service has similar things. It's worth thinking how you would feel about standing in the church and saying these things - but that is the sort of thing you'd talk about in preparation meetings.
Do you reject the devil and all rebellion against God?
I reject them.
Do you renounce the deceit and corruption of evil?
I renounce them.
Do you repent of the sins that separate us from God and neighbour?
I repent of them.
Do you turn to Christ as Saviour?
I turn to Christ.
Do you submit to Christ as Lord?
I submit to Christ.
Do you come to Christ, the way, the truth and the life?
I come to Christ.