C-x is a prefix key that often allows for many other commands in Emacs. These commands are always active (similar to M-x), meaning they can be used while in an interactive buffer.
Other prefix keys include C-c, C-h, C-x.
Using C-h after invoking a prefix key displays a list of commands starting with that prefix. F1 key can also be used. Helpful for getting a searchable list in the minibuffer
For example, to switch windows while in an interactive minibuffer you can use C-x o.