http://www.guitartricks.com/tutorial.php?input=426
Also you will want to learn about "Chord Leading".. I'm not sure what the correct terminology is for this because I did a quick search for it and couldn't find anything about it. It's very important to know what chord naturally leads on to another chord, makes things so much easier when creating your own chord progressions. For example, the V chord always wants to lead back to the I (root) chord. I have the list here somewhere...
I Leads To Any chord
ii Leads To IV, V, vii'
iii Leads To ii, IV, vi
IV Leads To I, iii, V, vii'
V Leads To I
vi Leads To ii, IV, V, I
vii' Leads To I, iii
Think of the most standard rock chord progression, the I-IV-V progression. The first chord: I leads to any of the other 6 chords, in this case IV. Now from IV it has to go somewhere.. it naturally leads to towards the I and the V but can also quite happily lead to iii or vii'. You can still go to the other chords but it's not usually going to like going there.. it's all a bit subjective really. For simplicity let's use the key of C Major. The first chord (I) will be C Major, the 4th chord (IV) will be F Major and the fifth chord (V) will be G Major. If you play a I (C Major) then a V (G Major) you will notice that there is an "unfinished" feel to the musical phrase.. this is what is referred to as unresolved tension. To resolve the tension, play the I (C Major) again.. see how it feels complete now.. like you could end the song on that chord?
Anyway..Start with the lessons on that link and let us know how you go..