Hello.
I'm total newb at Creation Kit, but was always fond of modyfing games. I like the possibilities CK creates, but one thing is not letting me having full fun from it. The problem is I can't edit my esps. When I create something, let's say a follower character (using it as example, because I wanted to make one for test) and I do something wrong, then I can't just open the esp and edit it (or can I?). I have to open the CK, load my esp along with Skyrim.esm and then I can do something. But after I fix the problem, I can't just overwrite this file. Okay, I can live with it. The real problem is that when I create new esp, with solution applied, then my character won't even show. I tried to use old esp as a master file, but I only get the old character, not the new one. Maybe there is some way to save work that I don't know? I'd be grateful, if someone would be able to help.

Cheers.

*confused*

If you create a new esp, and want to change it, yes you can simply re-open it in the CK make your changes and save/overwrite it.
What happens when you do that?

I suspect you've installed Skyrim in Program Files and are running into UAC issues. Move Steam and all your steam games out of Program Files.