These question is about maiden and married name..

I have a 10 y GC, SS number it is all in my married name...

if I file for citizenship....do I need to use my maiden name? or should I use married name?
what is the difference? what people do?

if I naturalize with my married name....what if in the future I need to change my name?

I'm trying to understand this thing about name changes.

My wife used her married name and then there's a space to put names used previously - that's where she put her maiden name. The form has an area for the current legal name and another area for name as it appears on the GC, so it seems plausible for someone to have changed their name after getting the GC. If you haven't changed your name since getting the GC, you should put the same thing on parts A & B on page 1 of the N-400. If you want to change your name in the future, I suppose you do it like any other citizen and file using your state's procedure.