The Lord Jesus was baptised
"And Jesus, when he was baptized, went up straightway out of the water..." (Matthew 3:16)
Baptism is ordained by the Lord Jesus
"Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:" (Matthew 28:19)
It's an act of obedience for believers and precedes fellowship
"Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls." (Acts 2:41)
"But when they believed...they were baptized, both men and women." (Acts 8:12)
Performed by full immersion under water
"...and they went down both into the water, both Philip and the eunuch; and he baptized him." (Acts 8:38)