This is really just for me so that I can remember how to do stuff in GIMP, in this case, it is how to outline stuff. This can be text, or just a selection

1. Open GIMP and create a new file (File -> New). Alternativiely you might be be editing a new image
2. Select the text tool (shortcut T) and add some text to your new canvas.
3. The light text color makes it hard to read on a white background. A dark outline will make it more readable.
4. Keep the text tool selected. Right-click the text-box you just created selected and select Path from text in the context menu (GIMP 2.8, older versions: Go to the text tool box and click "Create Path from Text")
5. Go to the menu Layer and New Layer. Make it transparent. Call the layer "text outline". :)
6. Go to the menu Select and choose From path. Your text will now be highlighted.
7. Now go to the menu Select again and choose Grow. Choose how wide you want your outline. Try 4-5 pixels.
8. Select the bucket tool (Shift+B). Choose the color your want for your outline. Use the bucket tool to fill the selected area.
9. De-select your selection. Ctrl+Shift+A or menu Select and None.
10. Now use the layer box (Ctrl+L) and move the layer with the outline down. You should now have a nice outlined text.