Earlier quoted context omitted.
In vim if you press K it will bring up the man page for the word under your cursor. It was very useful when learning C, considering that most libc functions have helpful man pages.
Note for people trying this at home, vim is case sensitive. I still regularly use this feature to look up libc and other things. You can also type 2K to go to ‘man 2’, or 3K to go to ‘man 3’ etc.
Many filetype plugins come with pre-configured 'keywordprg' settings. Including some non-programming filetypes like git which will execute `git show `, which is great if you're the type of person who often references commits in other commit messages.