like does it cost etc? (UK!)
It is a mailbox located at the post office. You can get one by applying at your local post office. They do cost, and the cost varies according to the size you want. The PO Box is very good if you want to get mail without giving others your home address.
You set it up by going to the post office, filling out some papers and giveing them a payment
It's a mailbox at the post office.