There is a https://meta.stackexchange.com/q/76566/295232 but it only covers URLs you'd normally don't find. I don't think there's a unified location document for 'public' URLs, so here's an attempt:

## Questions

- Canonical form: /questions/[question ID]/[question title]
  - Most links generated by the site itself have this form (e.g. question lists, sidebar widgets)
  - [question title] is not the full title if it's longer than 80 characters
  - What you type as [question title] doesn't matter; if you type something else, it'll still redirect to the canonical form (which exists [for SEO purposes](https://stackoverflow.com/q/25259/4751173))
  - If you use an answer ID instead of a question ID, it'll still work and redirect to the canonical form (of the answer)
  - Parameters ([here](https://meta.stackexchange.com/a/142535/295232) is an extended list, not sure if it's up to date):
     - `lq=1`: visited from the Linked Questions sidebar widget
     - `rq=1`: visited from the Related Questions sidebar widget
     - `noredirect=1`: prevents [redirection to original question](https://meta.stackexchange.com/a/125807/295232) (only active for anonymous users)
     - `lastactivity`: links to the last activity (edited post, new answer) on the page
     - `cb=1`: visited from the Community Bulletin (sidebar widget with Meta posts and blog links)
- Short form: /q/[question ID] or /q/[question ID]/[user ID]
  - This is the link you get by clicking the [share link](https://meta.stackexchange.com/q/63684/295232) underneath a question; the user ID is the one currently logged in, not the author. It makes sure the link counts for the [Announcer](/help/badges/74/announcer) badge and its kin.
  - If you use an answer ID instead of a question ID, it'll still work and redirect to the canonical form (of the answer)

## Answers

- Canonical form: /questions/[question ID]/[question title]/[answer ID]#[answer ID]
  - This is basically an extended version of the canonical question URL; again, only the question ID and the last answer ID matter (the latter because it scrolls the page to the right position).
  - The first answer ID matters if there are too many answers to fit on a single page; [it makes sure the correct page is displayed](https://meta.stackexchange.com/questions/155878/stack-overflow-url-format?noredirect=1&lq=1#comment448573_155882).
- Short form: /a/[answer ID] or /a/[answer ID]/[user ID]
  - If you use a question ID instead of an answer ID, it'll still work and redirect to the canonical form (of the question)

## Posts / revisions

- Edit post: /posts/[post ID]/edit
- Revision history: /posts/[post ID]/revisions
  - Can be visited via the 'edited x hours ago' link underneath a post, but works when there is only a single revision too.
- Single revision (rendered): /revisions/[post ID]/[revision number]
- Edit post, starting from a particular revision: /posts/[post ID]/edit/[revision GUID]
- Single revision (markdown): /revisions/[revision GUID]/view-source

## Comments

- Canonical forms:
  - /questions/[question ID]/[question title]#comment[comment ID]_[question ID]
  - /questions/[question ID]/[question title]/[answer ID]#comment[comment ID]_[answer ID]
  - Most of the remarks about questions and answers applies here, too

## Users

- Canonical form: /users/[user ID]/[display name]
  - What you type as [display name] doesn't matter; if you type something else, it'll still redirect to the canonical form (which exists for SEO purposes)
  - For your own user, this shows the Activity page; for other users, the Profile page
  - Navigation is possible with
     - the `tab` parameter (for the top tab: Profile / Activity and the second Activity tab (Summary / Answers / Questions etc.)
     - the `sort` parameter (for subtabs; sometimes it does affect the sorting, e.g. answers by votes or by creation date; sometimes it's just an additional filter, e.g. with votes)
     - the `page` parameter
- Shortcut to current user: /users/current
  - [Redirects to your own user page](https://meta.stackexchange.com/a/187935/295232)
- Short form: /u/[user ID]
  - [Even works for deleted users](https://meta.stackexchange.com/q/297554/295232) (♦ moderators are able to view them)
  - Doesn't support `current`
- Edit profile page: /users/edit/[user ID]
  - Normally only works on your own user ID; ♦ moderators can edit other users' profiles as well.
  - You can use `current` as user ID to create a link to your own edit profile page.
- Flag summary: /users/flag-summary/[user ID]
  - Normally only works on your own user ID; ♦ moderators can view other users' flag summaries as well.
  - You can use `current` as user ID to create a link to your own flag summary.