NO MATTER WHAT YOU DO PRESS THE SPACE KEY FIRST TO START ETCHING. IF YOUR BAT DISSAPEARS, EITHER PRESS 0 OR TRY REPPEATEDLY PRESSING L. Start out as the smallest bat on the screen. (If for some reason you can't find which bat is you, click on all of the bats and the one that say "Hello!" is you) First, if you want to etch as a bat, start using the arrow keys to go. You can change the size of your bat by pressing S to shrink and L to grow larger. If you'd rather etch as nothing (so normal etch a sketch) press the H key and then use arrows to control movement (if you want to switch back to a bat, press the number 0). To change size of your bat (if you chose to sketch as a bat) press the S key to grow smaller and the L key to grow larger. To change the color of your pen press the space key, and to change the shade of your pen press the P key. Click the green flag to erase your etch and start over. I would recommend etching in the smallest bat size possible, that way your character doesn't get in your way but you can still see where you left off. (P.S. as soon as you press almost any arrow key, a bat will start moving, eventually all three will move randomly about the screen)
I was originally trying to make a Mario game, but then I decided that would take a considerable amount of time, and since I didn't really have that I got the idea for an etch a sketch. P.S. this is the first scratch I've ever made, and the idea for it ended up being accidental (: