How does general delivery work?

General delivery worked very well for me when I was in college (in the 1970’s) and living in my car. I don’t recall asking for permission but it seems like a very good idea to let the post office know of your intensions.

A lot of people use General Delivery when they’re hiking the Appalachian Trail.
Not the Mark Sanford version, the real one.

My son took a six-month break from college to do some serious rock climbing and lived in a tent in Yosemite Park. His address was Name,General Delivery, Tent City, Yosemite Valley.

Years later I wrote a poem once about all the places he had lived since he left home at 18, which unfortunately (or fortunately, depending on your taste in poetry) I can no longer find. And I can remember having to change “valley” to “volley” for my rhyme scheme. (It’s probably a good thing I can’t find it.)