The template files phpBB uses are located in the folder called templates/ found in the phpBB/ folder in the folder in which you extracted the phpBB zip (or .tar.gz ) file. This is the folder where the file config.php is found. On your server you may have put the files from the root folder in another folder, perhaps one called forums/.

Note: I will from now on type folder names as with a trailing slash (example: templates/) and file names without a trailing, this is standard syntax and is good to know because its how you type file paths on most server operating systems. I may also refer to folders as 'directories'.

If you look inside the templates/ folder you will see at least one folder, most likely named subSilver. This folder contains all the template files for the default subSilver template which is the template included with all phpBB installations. It is wise to keep this folder, even if you create your own theme, since many MODs and other parts of phpBB depend on it.