The most referenced and most often used command on any Linux distribution is man, which lets users read the manual pages of other commands. Here are a couple of less well-known but useful commands that let you bookmark a position within a man page, and test a command you read from the man page without closing the page.
Man uses the less utility to display the manual pages on your screen. When reading through a lengthy man page, I often forget an interesting fact if I don't make a note of it somewhere before moving on to reading the rest of the man page. In such a scenario you can create a bookmark within the man page.