Answer 1

It's -kinda- like cookies in a way, but it temporarily stored in your browser's session. Basically, it's storing information for you while their browser is open, but if they close it and open it back up it'll be gone. Can be useful for holding something like a user being logged in, among other things you'll want to transition between pages. I'd research further into it though and get a good familiarity with it, it's very useful to know how to use.