There is a https://meta.stackexchange.com/q/76566/295232 but it only covers URLs you normally wouldn'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 but not up-to-date list, these are the ones I see the most):
- `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)
- `r=SearchResults`: visited from a search results page. In this case, a parameter `s=[rank]|[relevance]` is added as well; see [here](https://meta.stackexchange.com/q/242925/295232) for more details.
- `answertab=[sort]`, where `[sort]` is one of `active`, `oldest`, `votes`, makes sure the right sort is set (regardless of the user's current choice). Often combined with a `#tab-top` fragment to scroll down to the answers.
- 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)
- If you use the ID of a tag wiki or excerpt, e.g. https://meta.stackexchange.com/questions/62883, it will redirect to the tag info page.
- An obscure form, used in the newsletter: /landing/r/newsletter?cta=question&id=[question ID]
## 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)
- The global inbox uses this format (with `noredirect=1`) when somebody posts an answer to one of your questions.
## 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.
- The global inbox uses this format for notifications that one of your posts has been edited.
- 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
- Timeline: /posts/[post ID]/timeline
## 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
- Short form: /posts/comments/[comment ID]
- This format (with a `noredirect=1` parameter) is used in the global inbox.
## Users
- Most URLs support `current` instead of a user ID. This will automatically be populated with the user who is currently logged in, so e.g. /users/current will [redirect to your own user page](https://meta.stackexchange.com/a/187935/295232).
- 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 (for ♦ moderators, *all* users), 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
- 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`
- Flag summary: /users/flag-summary/[user ID]
- Normally only works on your own user ID; ♦ moderators can view other users' flag summaries as well.
- Edit profile page: /users/edit/[user ID]
- Normally only works on your own user ID; ♦ moderators can edit other users' profiles and some of the subpages as well.
- Edit subpages have their own URL structure, e.g. /users/email/settings/[user ID] for the email settings and /users/delete/[user ID] for the 'Delete account' page.
- Deleted recent posts: /users/recently-deleted-questions/[user ID] and /users/recently-deleted-answers/[user ID]
- Normally only works on your own user ID; ♦ moderators can view them for other users as well.
- Doesn't support `current`