can you please tell me which file i need to edit to edit the template - i
would like to add a banner code into the template (header) but i cannot find the
files to edit, only the css files.
It is best to go to Admin → Appearance → Edit Theme → CSS Because whenever you do an update (if you edit the files in master_pages; all of your changes will be lost. What exactly is the type of code you want to put in the header because you can do that by going to Admin → Settings → Main Settings → Page Settings