What does revoke access mean?
In one sentence: To cancel access you gave earlier, such as a share link or a badge, so the next visit is refused.
A little more
To revoke access is to cancel permission you gave earlier: remove a person from a shared folder, sign a lost phone out, or turn off a share link. The server forgets the permission, so the next request using it is refused. A revoked share link usually just leads to a not-found page.
Revoking only stops what happens next. Anything someone already downloaded, screenshotted or printed stays with them, and a copy kept in a shared cache could linger unless the page said not to store it. That is why it's worth checking what you share, and who it's for, before you share it.
It's a bit like… Changing the lock on a shed: old keys stop working, but anything someone already carried out of the shed is still theirs to keep.