To display a custom template, use index.php?custom=yes&TID=templatename . To display a pre-existing page using a different tempalte than usual, just tack on &custom=yes&TID=templatename to its existing URL.

All member variables for {THISMEMBER work in custom templates. Any type of toplist will work as well. If you wish to use a specific link, category, comment or member, just add it to the end of the URL of the page line this:

&linkid=1 (makes the link variables for link id #1 function on the page)
&catid=1 (makes the category variables for category id #1 function on the page)
&commentid=1 (makes the comment variables for comment id #1 function on the page)
&memberid=1 (makes the member variables for member id #1 function on the page)

As well, remember that the conditionals syntax works in custom templates the same as elsewhere.

If you want to set the title for a custom template, use Admin Panel -> Customizations -> Page Titles. If you want to make a custom template available at a simpler URL, see Admin -> Settings -> SEO -> Rewrite Other Specific URLs.