"Making an animation with the GIMP is an easy matter. It's the
same simple frame by frame concept you might have played with as a
kid, drawing images on different pages of a tablet and then
flipping the pages. All that's involved is making a number of
layers which will act as frames, putting them together, and saving
your work as an animated GIF."
"Begin by creating a new image sized 256 x 80. Add some color
using the fill or gradient tool. Open the "Layers, Channels &
Paths" window and make a transparent second layer sized 80 x 80
using the "New Layer" icon at the lower left. With the new layer
selected as your active layer make a selection using one of the
selection tools in the toolbox. Fill in the selection, again using
the fill or gradient tool. Remove or save the selection in
Image:Select. Now save as an XCF. You now have a rectangular image
with an object at the left."
"Right click the image, choose "Layers|Flatten Image" to combine
the two layers, and save as an XCF. Make sure to name it something
like "frame1" so you'll be able to identify the layers and put them
in the proper sequence later. Reopen your original image. Select
the second layer in Layers, Channels... and nudge the object to the
right. You can do this by hitting the "Move Layers and Selections"
button in the toolbox and moving the layer with your right arrow
key. Flatten the image and save as "frame2". Repeat this rather
tedious process until your object has moved all the way to the
right side of the image and you have a number of frames to work
with. How many times you do this depends on how many frames you
want. Keep in mind that making an animation can produce a rather
large file and that size matters, especially if you plan to use
your creations on the web."