The chord formula goes like this:
root note - whole step - whole step - half step - whole step - whole step - whole step - half step.
So, for the Key of C, you woudl have:
C - D - E - F - G - A - B - C
As for the actual chords, they go:
I - ii - iii - IV - V - vi - vii (dim) - I
Uppercase is Major, lowercase is minor. So, once again, in the key of C:
C Maj - Dm - Em - F Maj - G Maj - Am - B Diminished - C Maj
For each key, the place to start is with the Major Scale and the Natural Minor. The Natural Minor is taken from the 6th scale step. For each scale pattern, you will start at the root note.
Look up GUITAR SCALES online and you will find the patterns.
So, in the Key of C you can play:
C Major Scale (Root Note)
A Natural Minor (6th scale step of the key you're playing in)
Scales begining with other notes are called
MODES, and I wouldn't advise digging into them until you've mastered these first.
Hope that helps.