Help anyone?

I seem to be having some problems..ok so Im not the greatest with computers..but I have been trying to change my signature and for some reason I can;t ..and also when I try to post a picture it wont work?? I did go throught photobucket and keep getting error..saying either file to large or invaild..
when I try to change my sig..when I hit save or preview nothing happens...what am I doing wrong?