I recently read an article stating that to access Banff National Park, you need several permits: A park permit, a backcountry permit and, if you want to, a fire permit. I also read about these permits frequently on TGO, for example here and here.
For me, this system is completely new, since everywhere I visited so far things either had been allowed without permit or forbidden (maybe apart from fishing, but I never did that). In my understanding, a permit is something you apply for, and which can be declined.
How can I understand the concepts of these permits? Are they more like a fee or can the permit be declined? Do I get a piece of paper I need to carry around?
I understand some of the answers may vary for different types of public land, for the US and Canada or even for different national parks. I try to understand the general concept.
Also, I know this question is very close to the first linked question, When do I need a permit to go into nature?, but I want to know how this system works/looks like from a practical point of view rather than when I have to care about it.