Not sure exactly what you are trying to do, but here it goes:
1) If you are just looking to convert existing files .png or .jpeg or such into .gif, the Preview app in your Applications folder can do that under the Save As... command.
2) The shareware program
Graphic Converter will save as .gif...it has some painting tools in it, so if you are looking to create from scratch or edit an original before you create a .gif, that might help.