If you are an adult who has not been baptised a Christian, but are thinking about becoming a Catholic then the first step is to go to the local church and ask how they go about receiving people into the Church. Most churches are delighted to see new converts and will make you most welcome.
You will probably be asked to undergo instructions. Sometimes local clergy will do this themselves, other churches would have a programme, usually known as 'RCIA - Rite of Christian Initiation for Adults' to prepare people.
Generally you will get a more thorough preparation with an RCIA course.
Joining the Community
When you ask for Baptism you are asking to become a member of the Christian Community, the Church.
You would be expected to take part in the life of that community on a regular basis.
Like any community, hopefully you will find people there you get on with.
Dedicate your life to God
Traditionally Baptism is described as a sacrament which we dedicate our life to God.
When we make our baptismal promises we promise to do good and avoid evil. We are washed free of all sin and guilt.
The baptism service for adults is similar to child baptism except that you make the baptismal promises yourself.
Instead of godparents adults have sponsors whose role is to encourage you in the Catholic faith.
Traditionally adult baptisms take place during the Easter Vigil service. In some parishes therefore, you might be asked to wait for Easter.