I planned on doing a tutorial but I'm kind of waiting for Moeniir to release a new FLICster that will make it much easier to create new units (hopefully)...
anyway, to help you out a little, I would suggest using FLICster to separate an animation and get the palette and everything and if you want to create brand new units simply open the separated animation files and delete all but one frame and then erase whatever's in the first frame and start from scratch (make sure you use the 256 color palette that FLICster creates!)
As for formats... all animations must be FLC's, all still pics must be .pcx files. It doesn't matter how many frames the animation is, so long as there ar the same number of frames for each direction of an action for each unit. For example, each direction for the attack animation of the rifleman is 15 frames.