The Holy Bible provides clear direction on baptismal stages, who can be baptised and why.
In Matthew 3:11, the forerunner of King Jesus, said I indeed baptise you with water unto repentance, but He who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptise you with the Holy Spirit, and Fire. This refers to John’s role in baptising believers (adults) with water and his announcement about one who is mightier than himself who would baptise believers or adults with the Holy Spirit and Fire.
The believers must have heard about the stages of baptism, understood what they meant, make an informed decision about the importance or significance of baptism for their lives and family and subsequently, make a public profession of faith based on the baptism into repentance and become valid members of the Body of Christ.

Baptismal process:
The following steps describe water baptism.
In water baptism, elders accompany the believer into a river for immersion.
In a symbolic and public act of faith, a prepared believer with full heart and soul commitment to the Sovereign LORD enters a safe river.
Priestly prayers are offered by elders on behalf of those who need baptism.
During baptism, the believer’s soul is buried with Christ, raised from the dead in trespasses and sin nature, and clothed with the NEW MAN. Christ is the only one who can raise us from the dead into eternal life.