GIMP HELP!?!?!?!? HOW TO DRAW?

i might sound like an idiot by saying this but.....how do i draw in G.I.M.P??? i just downloaded it so idk how to do anything. i just wana start drawing with a pencil like in ms paint. how do i do that? i click on the pencil icon in the toolbox and i try to draw on the layer but i cant? HELP!?!?!?