Template – template to do this?

Hi,

also I have a problem understanding the template system in nextgen gallery. I was reading a lot of posts and all the interesting posts are not answered. So I try it again:

How das the template system in nggallery work?
I do have to copy some files, but I don’t really know how to change them.
So, is there a possibility to provide me a working php- and css-file with some changed frames around the pictures, so that I can try to understand how that works?

Please help me, I have been looking for a solution for a long time.