Sorry that this is a link to an article that then sends you to a few other places.
But it is worth it if you want to understand the new landscape for federal campaign contribution law. And, it includes a bonus of a handy chart to help distinguish between a federal PAC, a party PAC, a 527 and a 501(c).
You kinda have to care about the dirty details of campaign finance. But if you do, this is a great tutorial.