Hey JJR:
Welcome to the Boards... These are easy, laid-back boards and no one is likely to start kicking your guts around here... Feel comfy here.
Now that you have just turned 21, it is only logical that you are looking for some sort of a relationship, ranging from 'A Try ONS' via 'Friends w Benefits', 'Buddies' or more.
It might be a trifle too soon to put a definite label on your sexuality, and seriously stick with it. If you feel that you are basically bisexual, let that be your 'working theory', but not something that you would want to see as the final truth about yourself, and proclaim to the rest of the world at this stage.
Judging by your question, I'd say that you feel like exploring your 'gay side' at the moment. Open your mind, sharpen your senses, observe well, AND get going. Put a profile or two on some of the dating sites. Hit a few bars, clubs or even spas. Be reasonable, stay safe, AND by all means enjoy life.
All the internet boards that I am aware of, including this one, are actually language-based communication platforms. We TELL each other that we are gay, str8, bi, pan or whatever. How else would the others know, where we are coming from?
Real life is somewhat different. People will invariably assume the 'situational concept', i.e., if you are having a drink in a gay bar, all those around you will want to believe that you are a gay man. They will hit on you, and you are kinda expected to hit on them, too. That's why most people go to such places. I would pick it up from there, and see where this takes you to.
I would stop short of starting a convo with "Hi, my name is JJR,
and I am 'bi'." First off, because this will sound totally dorkish. No one talks like that at such places

; Second off, you are a bit too young to really tell for sure; Third off, no one really cares.
Guys who you meet online, at the bars, clubs, sport clubs, gyms, libraries, etc., know that your life history (in terms of your sexual orientation) most likely does NOT begin with them on that day. They also know that they cannot really change your past, and I guess, very few people would really have any reason to want that.
So, both of you start from the situational concept. If you met a dude in a gay spa, assume that he is gay, that he assumes that you are gay, and that no one really cares too much about your possibly complex past. (People call this 'luggage', and they really do not want too much of that.) Pick it up from there, and see where this takes you.
You are neither marrying the guy nor are you promising eternal fidelity to him nor anything at that stage. Go, one step at a time...
If and when you reach the stage of planning a common future, and if you even at that time still feel your 'bi-interest' undiminished, share that truthfully with your partner.
Keep in mind that there is a number of gay guys who are very resentful of the 'bi' men, mostly because they fear being dumped for 'a chick'. This is, of course, a patent idiocy. If a dude ain't happy with you, he'll dump you for a chick, for another dude, for a period of solitude, for a fleshjack, or an oversized dildo, and/or any combination thereof.
KD