How can I add a breadcrumb trail to the top of every page of my site? I wait to to look like: "You are here: (page name)"
Try a breadcrumbs plugin. Breadcrumb NavXT is a popular option I believe.
An alternative solution of is just printing the name of the current page. Here's what such a function might look like in its most basic form:
Note that this will only work on single pages (posts, pages, media and custom post types etc.), and you'll have to add some logic to display titles for archive pages.