Step 1: Go to icanhascheezburger.com to see some lolcats.
Step 2: After having seen the new lolcats on ICHC, you desire to see more. Head on over to cuteoverload.com.
Step 3: Surf Cute Overload and watch a couple of videos, including this redonk video with kitties looking at stuff.
Step 4: Continue surfing cuteoverload and watch this video where a cat is playing with a theremin.
Step 5: Wonder what a theremin is and google it.
Step 6: Read the excellent Wikipedia article on the subject.
Step 7: You have now learned what a theremin is.