Using gimp and blender?

I have seen a lot of videos and they are done with blender and gimp, so how can you edit an animation with gimp and is there some tool what makes same effects to all frames?

You can download the GAP (gimp animation plugin) then use that. I’ve not tried it, though you may find a link to download a copy here:

VirtualDub is able to apply the same effect to all frames of an animation, be it resize, resample, smooth filter, etc, etc.