Where are my files I can modify?

Hello,
I am new to the vshare world so this is probally a silly question for some but here goes, I am needing to modify the templates and I am looking for the code. I bring my site down in dreamweaver but all .php and .html code is in binary. So where can I go to make mods If I cannot change the code itself? All I want to do is add different colors and place ads in different places without using the ad thing in the admin panel? I am new to this type of thing , modifying an existing template so any help would be appreciated.