Modding your Av box?
 

I don't know exactly what it is called, but I'd like to put something that is in the User's Profile under their avatar like their location is already. How can I do this?

You would need to edit the appropriate template via the vbulletin admin control panel, and add the variables you want into it. If you say, what exactly do you want to put up there, you might have a better chance of getting a straight-to-the-point answer.

it's a field I added to the profile, but if I knew which template to look for, I could probably figure out how to get the field in there.

The template you need is:
MEMBERINFO

And to add additional fields you use $profilefield[fieldX]