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A 'legitimate' Buddhist really only needs one things: To follow the teachings of the Buddha. All else is really just ritual. But if you want to make some sort of pledge about it, I recommend taking refuge in the Three Jewels - and meaning it. That's how I did it, that's how many others have done it, and it seems to be working out just fine. 3nodding

Certain sects may have specific rituals they want a follower to go through, so if you follow a specific one, you might want to check them out as well and see if there's a ceremony or something you might want to undergo, but as I said, it basically just boils down to following and believing in the Buddha's teaching.

Edit: Also, moved to the Questions and Answers subforum. 3nodding

Not to say you are this way, but your age causes me to say this. You should be sure this is what you want. Many in media make it look easy, but it isn't. The 8FP; Right view, Right intention, Right speech, Right action, Right livelihood, Right effort, Right mindfulness, Right concentration, they're all important and must not be taken likely. Be sure you have the discipline to follow through, otherwise you'll just be wasting your time.

That gloominess out of the way, to join you must only decide to join. There is no official conformation like in say the catholic church. Some sects have ceremonies.... sometimes. Just accept your choice, and be mindful of yourself.