Watch the Arpeggios & 7th Chords online guitar lesson by Stu Hamm from Stu Hamm U: Fretboard Fitness

Here is some basic theory for you. This lesson will show you where all of those chords with the little funny numbers after them come from. 7th chords are made up from the root, 3rd, 5th and 7th notes of whatever scale you are playing. The 3rd, 5th and 7th tones vary in each scale or mode, the 6th being flatted in the Dorian mode while being natural in the Aeolian for example. Try to get this idea in your head and you will get a long way down the road to de-mystifying the modes, 7th chords and chord-scales.