microsoft dynamics webAPI listing purchase orders

Question

How do you list purchase orders using the Microsoft Dynamics WebAPI?

Similarly, how do I list purchase orders with their line items using WebAPI?

I am having a real hard time finding decent and clear documentation on using WebAPI to find purchase orders, and especially purchase order line items, so any help would be appreciated. I just need a good starting point. Even some library would help, as I could look at what the library is doing and maybe try to mimic it.