I'm new to multiplayer (last i played was back when Vista was still being used, not fun). anyway, i'm asking because i don't use the Mic often with my headset, is it required or can i just use chat? in addition, why is it that when i do chat, no one responds? it's just radio spam. thanks in advance.

Do i need to be in a team here or what? what do i do?

I don't think it's necessary most of the time. I never bother plugging a headset in and it's only recently I even noticed anyone using VOIP, mainly two man attack heli teams. It's quite rare for anyone to use their mic to talk in squads nowadays, I just type if I need to say anything, personally.

Usually when we play as a team we bunch up on TS. It's free for all and easy to use (voice controlled or ptt!
I find that it is hard to follow the in game chat while i try to survive in the virtual field, so yes, voip is better if you want to be recognised.
You don't need to be in a team, but i will recommend it especially if you are "new" to the game or the server. The more expereanced guy often like to lead a squad and be a good base (spawnpoint) to stay in game and do something usefull. But all this is sure only my opinion. Heal you later @Ripper .

P.S. This is not Project Reality and nobody will look or point on you if you don't talk back on voip or respond in chat or play all alone.