Or I can put up a downloadable version of Photoshop for everyone to enjoy
Basically you use imaging software and you save out the image in a gif format. So let's say there's a picture called "adora" that you made. You would (usually) click - in the prgrom your using - File>Save As>adora.gif
So the ".gif" is the extension thelling you what format it is in.
"adora.jpg" is another format for pictures.