I notice when I doenload a theme pack That it comes with several folders.
Blocks, themes, and extra graphics.

Well I know what the other 2 are for, but what is the file in the blocks folder for i.e. block-subBlack-Forums.php

Everything seems to work fine without me adding this file, or am I missing something by not uploading it to my site?

Sorry so n00bish

The block that is in there is for the last five forum posts. If you don't use it on your site, then don't worry about it. It's included because a lot of people use that block.