show/hide html depending on variable

How would I do this?
I'm new to TBS but I have had experience with the phpBB template system (yes totaly different I know) but is there a way of showing or hiding whole blocks of html if (for example) a user is logged in or logged out.
I.e. when logged out in the side menu there is a login form
when logged in, in the same side menu in the exact same place is a welcome message showning user details?

Hi DJMoran

Take a look at the examples on lines.
See "conditional display".

Thanks, I couldn't get my head around it at first