I suggest you also check out the website by our very own Trent Austin:
Unlock Your Talent!
As for the I, IV, V stuff, that's a reference to the position of the chord in relation to the key you are playing in. In other words, take the key of C. Looking at the C scale: C, D, E, F, G, A, B, C. Now number the scale, I, II, III, IV, V, VI, VII, I. If the chart says I, then you play the notes associated with the C chord. If it says IV, that would be the F chord, V would be the G chord.
Staright ahead rock 'n roll is based on I, IV, V chord progressions, for example.
There, Ive now totally exhausted my knowledge of music theory, I'm running out and getting that "Idiot's Guide" too.