If you do make or eliminate prefix keys, that changes the set of possible key sequences. But F1 should work for all prefix characters. 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.
The bindings between keys and commands are recorded in various tables called keymaps . See section 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. Rebinding keys is a common method of customization.