Post Indexing Does What?

Ok. I’m sort of clueless, but I’m guessing the Post Indexer plugin makes it possible to do something like MarketPress does where each person has their own posts on their subsite and they can all show on the main site.

How do I do this using the plugin? All I have done is installed the plugin and created a few posts on a sub site to see where they show up and I can not find it.

I would like to do what is done with MarketPress except just with regular posts and a Custom Post Type.