Look at skin1/customer/categories.tpl
You'll see a capture start:
Code:
{capture name=menu}
A bunch of junk in the middle, and then a capture end:
Code:
{/capture}
{ include file="menu.tpl" dingbats="dingbats_categorie.gif" menu_title=$lng.lbl_categories menu_content=$smarty.capture.menu }
This code calls menu.tpl and passes the variable menu_title to it.
Menu.tpl then puts a frame around all the junk between capture start and capture end using the menu_title variable that's passed to it.
Make sense?