Among Christians there are two kinds of baptism: Water baptism and spirit baptism. I’ll talk about spirit baptism elsewhere.
Water baptism is, basically, the sort of baptism the prophet John did. John preached a baptism for repentance. (Mk 1.4) You want to repent your sins and turn to Jesus. And how you represent that is with water baptism. You get washed.
Baptism is the formal Christian initiation rite. Once you turn to Jesus, you get baptized. If you’ve never been baptized, you need to be.
Is it a requirement? It actually is. True, Jesus never ordered His followers to get baptized. But it is part of what God wants for us. (Lk 7.29-30) Jesus did tell us to baptize new disciples. (Mt 28.19) And if you’re gonna follow Jesus, it also makes sense to follow His example—and one of the things He did, as our example, was be baptized.
In the bible, the folks who repented and turned to Jesus were baptized as soon as Jesus’s disciples could get ahold of water. The idea is supposed to be that the baptism represents the new life in Christ. So much so that the early Christians equated the two—you turned to Jesus; you were baptized; these things happened as close to the same time as possible. (Ac 2.38) That’s why sometimes certain verses look as if we’re saved by baptism. (Mk 16.16) When Peter told the Asians that baptism saves them, his point was not that getting washed saved them, but that the Christian’s response to God is what’s important. (1Pe 3.21)
Some churches say baptism isn’t a requirement, and really they’re erring on the side of not being legalistic. They don’t want to force anyone to be baptized: after all, you’re not unsaved if you never get baptized. The thief crucified next to Jesus went to Paradise without a baptism. (Lk 23.40-43) Still, it’s not a good idea to start off a new Christian life by refusing to fulfill your very first obligation. If that’s the sort of relationship a Christian intends to have with Jesus, maybe they ought not bother to call Him Lord at all.
John didn’t invent baptism. Baptism, which the ancient Jews called a mikveh, was ritual washing. Before they went to temple or synagogue, they needed to be ritually clean. So they put on clean clothes and walked into a pool of water—either a nearby river or pond, or a pool they kept near the house; someplace with running water. They walked in until their heads were covered, then they walked out. Baptisms vary, depending on the church—some sprinkle new Christians with water, and some dunk them in a pool or river—but, apart from some Messianic Jewish groups, none of them look like a proper mikveh. Personally, I don’t think God is particular. But plenty of Christians will disagree with me.
Some churches practice infant baptism: When you’re born to Christian parents, you get baptized. They assume that if you’ve got Christian parents, they’re gonna raise you Christian, so you may as well be baptized. Once you’re old enough, you can have a confirmation ceremony, and formally state that yeah, the baptism counts: you are a Christian. Of course, the baptism has to count on God’s end, but what you’re confirming is that it counts on your end: You really do want to repent of sin and follow Jesus.
Other churches practice adult baptism (or “believer baptism,” since they’ll baptize children): They insist every Christian needs to decide to follow Jesus before they’re baptized. Babies can’t do that, so they won’t baptize babies. However, they will baptize children who appear to understand what baptism is. They usually expect you to make some formal statement of faith, like your testimony or “Jesus is Lord,” and then they’ll baptize you. (If you’re at a church that practices infant baptism, but you were never baptized as a baby, they’ll baptize you as an adult in pretty much this same way.)
Churches that practice adult baptism are usually insistent that infant baptism doesn’t count, so if you’ve been baptized as an infant, they’ll insist on baptizing you again. Do you need to be baptized twice? Can you be baptized twice?
There’s actually nothing in the bible that says we can’t be baptized again—and again and again and again, if you want to be. If you want to be baptized every Sunday morning, honestly there’s nothing in the bible against it. The trouble is that baptism is our Christian initiation: It’s what you do when you first become a Christian. It’s not what you do every time you screw up and repent. It’s not what you do whenever you think to yourself, “Wow, I didn’t understand Christianity (or baptism, or religion, or whatever) before, but now that I do understand, I need to get baptized again, to reflect my new understanding.”
No, you don’t. You really don’t. When Jesus’s students were first baptized, all they knew of baptism was what a mikveh was, and what John told them about repentance. Then Paul came up with this profound, Holy Spirit-inspired insight as to how we died to sin, and how baptism joins us to Jesus, and to His death. (Ro 6.2-4) Paul’s idea isn’t anything like John’s idea; it’s just a different dimension to baptism. But after the Spirit revealed this to Paul, did it mean that all of Jesus’s original disciples needed re-baptism? No. Same with you. Add your new knowledge to your old. Confirm, re-confirm, and re-re-confirm, that original baptism. There’s always gonna be more to learn.
If it helps, think of it like ritual circumcision: Once is plenty. Re-baptism might make you feel good about yourself, or better about yourself, or feel like you’ve achieved something. But really you haven’t. It’s not wrong, but it’s not productive. Infant baptism included.
Okay, so how do you get baptized?
If you want a formal ceremony, ask your church. They’ll probably make you attend a “baptism class.” Some churches won’t baptize you till you take it. Baptism is a profound thing, and in order to make you know how profound it is, they’ll make you sit through a class where they tell you so. They’ll tell you everything I just wrote, only longer. There actually isn’t much detail to baptism: Repentance, death to sin, Christian initiation rite, everyone needs to do it, and why God is in favor of their method. (And sometimes why other methods are bad.) Realistically the class shouldn’t be more than a half hour. But some churches have managed to stretch the class into weeks… despite plenty of biblical examples where people were baptized without taking any class at all.
But if you’re not so formal, any Christian can baptize any newbie. So go find another Christian and ask that person to baptize you.
If you prefer dunking to sprinkling, you’ll need something big enough to be dunked in. The ocean, a lake, a river, a swimming pool, a hot tub, or even a bathtub will do. If you don’t care, you can be baptized with a bottle of water.
Get the water in a place where you’re gonna get wet by it. Tell the Christian that you’re doing this because you’ve decided to follow Jesus and you recognize He’s Lord. Have the Christian say “I baptize you in the name of the Father and the Son and the Holy Spirit.” (Mt 28.19) The Christian can either pour the water, or dunk you in the water, or whatever you need to do to get wet.
And that’s it. You’re baptized.
Everything else is just padding. If you want the padding, there’s nothing wrong with it. Take the baptism classes, do it in front of your entire church, share your testimony, make a video. Just don’t wait too long. Baptism is initiation, and it’s kinda stupid when your initiation rite takes place years after you turn to Jesus.
As for those people who are extremely agitated right now ’cause I didn’t recommend their own particular favorite kind of baptism, or who think I’ve oversimplified things, or emphasized the wrong stuff: Correct me in the comments. But I think I’ve hit all the points made in the scriptures. Everything beyond the scriptures—everything that comes out of our church traditions—is open for debate. So debate away.