Watch the Day 9 online guitar lesson by Ravi from Learn Guitar in 21 Days

You have already been playing three chord songs in the key of A, using the chords A-D-E. Now, you can play those same chords in the key of D, using D-G-A (for you theory buffs, that would be a I-IV-V in the key of D).

You might find that one key is better than another for your voice, or that it simply sounds more like the original. Having such options really puts you in the driver's seat in terms of getting the songs and sounds you want out of your guitar.