GIMP WON'T DRAW ANYTHING -- WHY?

No, sometimes you select a drawing tool, your color and brush are set
properly, and GIMP just won't draw anything!  Unfortunately there are
lots of reasons this can happen.  Here are some things to check:

- If you have a selection, gimp will only draw inside it.
  So check whether you have one, perhaps an invisible one:
  check View->Show Selection and make sure it's checked (so you'll see
  the "marching ants" wherever there's a selection), and then, to be
  sure, do Select->None.

- Check the Layers dialog.  Is the right layer selected, and visible?

- Check the Tool Options for the tool you're using.  Many of these
  tools have a "Mode".  You want this set to Normal.  If it's set to
  anything else, then what gets drawn will depend on what's
  underneath.  Sometimes this can be cool (try some of them,
  if you want!) but sometimes it means that nothing will be drawn.
  The discussion of modes in the GIMP manual is at
  http://docs.gimp.org/en/go01.html -- search for "Layer Modes",
  which is under M, not L; another good page if you're curious about
  modes is http://www.pegtop.net/delphi/blendmodes/

- Layers also have a mode.  Go to the Layers dialog and make sure the
  Mode there is Normal as well.

- While you're in the Layers dialog, make sure "Keep Transparency"
  isn't turned on for this layer.  That's the checkbox to the right
  of the Mode option menu; in Gimp 1.2 it's labelled "Keep Trans."
  but in Gimp 2 it only has a little checkerboard next to it.
  You want this NOT checked, for now.

I recommend that you keep this list handy.  You WILL find times
when it doesn't draw and you're not sure why, and you will probably
forget some of the possible things to check.  At least, I do.
If you find other reasons that I haven't listed, please let me know!