[SOLVED] 3.4: Confused: body title versus meta title

Forgive me my SEO ignorance here, but I don't understand the difference in body title and meta title, except that when you type in a meta different from body, the meta displays as the title in the browser window/tab. If left blank, the body displays. Meta keywords and meta description do make sense to me, but what is the concept behind meta title? Can someone explain whether and why I should fill in something here? Thanks. And BTW, I'm not using any other SEO plugin besides what is built-in to the theme.

EDIT: Just a couple of questions that came to my mind after I wrote this:
Should the meta title be different from body title...why or why not?
Should I add my categories and tags as keywords?

EDIT: I figured it out myself