1- Drag and drop the AVI file into anim shop (or open it). You already can give some parameters in the appearing window but simply click OK because you can change them later too
2- You can arrange the animation before you create the gif : culling it, resize it, replace colors, add effects and so on... through the different cool options of anim shop...
3- File --> Optimization Wizard : Here you can select your output format... --> gif
)Then you click on next... next... next if you only want to transform the avi file into gif without changing anything ! You save... finished !!!
(OR you can change the number of colors to reduce the kb for example... before you save ! The best way is to test the different options... you accept them or you click "back" and you retry...)