Picnik.
It's actually really good. They try to make you go pro by makign things unavalible to free users, though. Cheap way to try and make money. But it's a nice editor that looks professional if used well.
I don't understand the layers, or much of anything . . . not a techy person . . . I've been using picnik for most of my pictures =/.
What's just anything I need to know?