Couple questions about keybindings (^x ^ctrl, press any key, ect...)

What ^x (or ^ctrl) does mean? - I found this in keymap-manager’s source code.
What best solution for “press any key?”.
Is it possible to register “any key” for bindings (i.e. ctrl- p x)?
Do the Atom need a combination with any key? For example, in Vim, there are such combinations (f <any-key>, v i ['"[{(<] ...).