I have a PO box that I will be using to receive my packages, but when I check the address on the receipt from when I bought the PO Box, the zip code is different than the zip code of the post office. Is this normal? How do I know that I'm sending the right address? Should I just include the address of the Post Office as well as the PO Box number?
No, that's actually normal. The PO Box I use has zip code xyxwz whereas the actual post office it's in is xyyxq. All you need is
FirstName LastName
PO Box #xxx
City, State Zip Code
USA