Clarify "action character is followed by a string"

[onetom]

The README.md says:

When using ace-window, if the action character is followed by a string, then ace-window will be invoked again to select the target window for the action. Otherwise, the current window is selected.

I've read it many times, but I couldn't figure out what does it mean.
Is it referring to something like:

(setq aw-dispatch-alist '((?a "<string>")))

or it means if I run ace-window, press an action character, then I just start typing letters?

I was hoping that somehow I can do M-o x/v/h RET do delete/split-horizontally/split-vertically the current window and these sentences from the documentation seemed relevant.