Scales vs Keys

Which Scales do I play over specific keys...for example which scales would I play over the key of A.

Assuming you mean A major....you could play any scale in that key: A Ionian, B Dorian, C# Phrygian, D Lydian, E Mixolydian, F# Aeolian or G# Locrian

I see like yea you would play those over A...i mean how do I know which scales to play over which keys...

even books or videos just say "here a pentatonic scale...ok now play along" but one pentatonic scale only works for one key.

other tutorials say 'play this over a chord' but that isn't really right as you would play something different over that cord depending on what key it's in

its just so frustrating to me because on those rare occasions when I find the right scale i can blaze out some KILLER licks but all the rest of the time i sound like crap

thats just a matter of knowing the notes in each key. for example, the notes in the key of A major are: A B C# D E F# and G#. check out the lessons section of this site, there are a few very good lessons talking about keys and scales and modes and such.

in fact, check out the very first lesson at the bottom of the lessons page that bodom did.