Animated gifs actually contain a series of images (or frames) that are displayed one after the other and give a semblance of animation, just as in traditional animation techniques. Also, in animated gifs you can control the time for which each frame is displayed. Look at the image below.

The image consists of 8 frames each playing for 10 milliseconds each.

Frame 1 : 10 milliseconds

Frame 2 : 10 milliseconds

Frame 3 : 10 milliseconds

Frame 4 : 10 milliseconds

Frame 5 : 10 milliseconds

Frame 6 : 10 milliseconds

Frame 7 : 10 milliseconds

Frame 8 : 10 milliseconds
 

Our animated gif of a running dog (above) starts at frame no. 1 which plays for 10 milliseconds and then frame no. 2 is displayed and so on. When the last frame (no. 8) is reached, the image loops and displays frame no. 1 once again. You can specify the number of loops you want in the animated gif or you can set it to loop indefinitely.

In the above animated gif example, each frame is played for 10 milliseconds. Now, let us change this to 25 milliseconds as in the image below.
You will notice that the dog has started to run slowly and its motion is jerky because the frames in the animated gif are displayed for a longer period (25 milliseconds instead of the 10 milliseconds like in the original). If you want to create a slow running dog but with smoother motion you would have to create many more frames especially those that go in-between the start and the end frames.
 

How to create animated gifs

Animated gifs can be created or modified using any of the freeware or shareware available.