Take a song you like. start with something that sounds fairly simple but good melody. Tab out what chords you sing over what words. If you're not ready for this find a friend, down load a tab, or buy a book.

Check out the key. See what chords they are using in the song.....
Major key I ii iii IV V vi vii* key of C is easy to start with no sharps or flats

CDEFGAB C=I, Dm=ii, Em=iii, F=IV, G=V, Am,=vii, Bm aug.=vii (I think thats right for the Bm chord)

In any case this gives you the chords that fit key of C. you'll find that I>IV>V and variations of the order of these major chords are in tons of songs.

Look up the interval between chords whole step 1/2 step for major minor keys and you can figure out what chords are used in any key.

Hope that helps and not completely confusing.

S