You don't get to see the source. If you intend to keep it and continue using it, you must pay a fee. You don't get to see the source. And you can redistribute it with the same conditions for the new user. BSD Software is free.
Source is open.
You can basically do anything to it that you want, but you have to give credit somewhere to Berkely when you use it. GPL Everyone can have it for free. You're not allowed to modify it though. Basically the code comes free. According to ESR, the whole point of the software industry should be service, and not sale value.