I was explaining the differences between the two licenses Paizo offers to a friend of mine the other day, and I thought a quick summary of them would be helpful.

The Compatibility License is for professional publishers who want to make money from their products. This lets you use the Pathfinder (or Starfinder, which has its own similar license) rules and claim compatibility with the game. You don't get to use any intellectual property (or, properly, "Product Identity") in them. So you can write a new class, or a new adventure, or an entire game world with this license, but you can't use Golarion, Iomedae, Sajan, and so on. You're basically prohibited from using proper names. You can find the whole license here for Pathfinder Second Edition and here for Starfinder. 

The Community Use Policy is for non-professionals who are putting things out there for free. You can not only use the rules, but you can also use the Product Identity. That is, you can tell stories set in Golarion about Iomedae and Sajan. You can also use some of Paizo's art (but not its maps); generally, any art Paizo has put up on its blog, which is a LOT of stuff, is available to you. What you can't do, though, is make any money; you can't charge anyone any amount over your base cost to produce something (if it's like a book). So you couldn't charge for a download, for example. You also have to clearly state that Paizo isn't endorsing your product or use of their intellectual property. You can find the whole license here

Even more succinctly: you can set your product in Paizo's worlds, or you can sell in for profit. But not both.

Here's a nuance. A single individual might use both licenses, for different types of products. But be wary when crossing the two streams. Your free, in-world product might be considered an improper commercial use if you're using it to advertise your for-profit commercial projects under the Compatibility License. It's best to keep both uses entirely separate. For example, the products I have here are all published under the Compatibility License. This is commercial work. I do produce materials for fun under the Community Use Policy, but that's a different website entirely and I don't think I've ever cross-promoted one to the other (and, no, I'm not about to do so now).

Keep in mind what you want to do, because it determines which of the two licenses you should use.