I have figured out how to put photos into a shared photo stream folder within the Photos app, however, I can't actually figure out how to get someone to subscribe to my Shared Photo Stream or how I would subscribe to someone else's?
You have to be invited to subscribe to somebody else's.
To add subscribers, go into gallery, tap photo stream, then tap the edit button at the top right (iPad) then tap the photo stream you want to edit, or on the iPhone tap the blue arrow next to the photo stream you want to edit.