Actually it is quite easy, you put the stages of the animations in different layers, when saving you chose gif and enable save layers as frames, after that you get to a window where you can choose some things, as how fast the pictures will change.
I am sorry if i don`t use the right words, this because i am using the german version.
edit: I don`t know whether or not the window is a part of Photoshop or a stand alone program, but it looks like a part of the program for me.