Starting

Ok, I'm gonna assume you're all beginners, and start with the basics.
So, Greetings:

Good Morning = Bom Dia
Good Afternoon = Boa Tarde
Good Evening = Boa Noite (it's also used as "good night" when you're going to bed)

If you wanna ask someone if he's doing fine, you can ask:

Como vai? (literaly means "how are you doing?")
Tudo bem? or Tudo bem com você? ( it would mean "everything ok?" or "everything ok with you?"

To answer this, you may say:

Tudo. E com você? ( "everything (ok). how about you?)
or Tudo bem. E com você? ( "everything ok. how about you?")
Sim (that's "yes")
Não (that's "no", even if its sincere, it may sound rude. be careful)

Bye = Tchau
See you = A gente se vê
See you soon =  Até logo
See you later = Até mais or Até mais tarde
Bye, kisses = Tchau, beijos

Brazilian people, men and women, use to greet themselves with a kiss on the cheeck. Actually, you lean your cheek on the other person's cheek, and kiss the air. You can do this even when you meet somebody (not for job or, your boss ok?), you don't need to be friends or have intimicy. Important, guys dont do that on guys. Girls do on guys and girls. Guys just do it on girls. Remembering the age is not a problem here. If you're a man, and you greet other man, you shake his hand, even if you're young.