Animated .gifs can start out as almost any visual format- photos, text, clip art, line art, charts, diagrams etc. You'll need three basic program tools to animate, a graphics editior, an image optimizer and an animator.  You could use a separate program for each item, or choose one program that can do all three steps. 
Animation is the art of fooling the eye that two or more pictures called animation frames, with small changes and viewed rapidly, equal motion. 
The red arrow has only three frames while the gold exploding rocket has 6. The yard tool animation with fades has 11 frames. 

Content and clarity of thought should reign supreme on your pages, after all the whole purpose is to convey information. It is still absolutely true that content is king! Animation is best used as a way to clarify a point, show a visual representaton of an idea, or carry out your design theme.

Two good reasons not to use excessive animation is that it takes longer to downoad animations than a single picture or no picture, and unless you create your own animations, you seldom find one that conveys a true enhancement of a printed message.
 

Do you just love old Warner Bros. Cartoons? Looney Tunes and Merrie Melodies? Bugs Bunny, Daffy Duck, Porky Pig, Foghorn Leghorn? Most people do, but some of us carry it to, well, almost an obsession. 
For those who fall into this category, I recommend the Warner Brothers Cartoon Companion, a searchable, alphabetized, thoroughly cross-linked database of Warner Bros, cartoon history. It's found at Spumco.com, the online site of "Ren & Stimpy" creator John Kricfalusi, aka John K.