I am new to pc gaming and really the whole pc scene. I am very unsure about some things like if i buy a game off amazon and download it could i still play with someone who bought the game on steam or does it not work that way?????

I'm not aware of any games that segregate their multiplayer between Steam and other DRM methods. You'd have to check the game you're buying to make sure, but I'm 80% sure you don't need to worry about that.

like i saw that amazon is having a huge pc game sale and trials evolution for pc is only 9.99 but on steam is 19.99; so it wouldn't matter if i had it downloaded ot my computer or steam?

It doesn't matter where you get the game when it is on PC.

Yes, you can play together regardless of where you bought the PC version of a game. In general, buying a PC game from different sources (Amazon, Steam, etc.) is a bit like buying a console disc from different retail stores. Different stores may have different prices or policies, but as long as all copies in question are made for the same platform (e.g. PC version, 360 version, etc.), they are all compatible regardless of which store you bought from.

Most Amazon codes are actually redeemable in Steam. Not going to say that all of them are, but they usually are.

Also EA games bought digitally on Amazon are usually also retrievable on Origin by entering the game's product key.

Thanks fro the help every one, i really appreciate it a lot. when you say amazon code is redeemable on steam what do you mean. sorry for my lack of knowledge i have been a console gamer for too long.

When games are redeemable on steam, you will get a key from amazon and activate it on steam. That's usually the only way you can play the game if it is activatable on steam.