This manual is full of passages that tell you what particular keys do. But Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named commands , and then gives keys their meanings by binding them to commands.
Every command has a name chosen by a programmer.
For more information on commands and functions, see What Is a Function . The bindings between keys and commands are recorded in various tables called keymaps . See Keymaps . It is the command next-line that is programmed to move down vertically. C-n has this effect because it is bound to that command.