By default, I think you can press (num pad) keys 1 and 3 for left and right rudder. 5 centres everything.
Using settings, keyboard, all, flight controls, basics, rudder (l/r/centre) you can assign keys. Obviously, you can also assign buttons on your yoke.
Also, to address the second part of your post, I'm also reasonably certain that rudder control is automatic in flight if it's not assigned elsewhere or if no rudder pedals are attached.
This is for X Plane 11.
PS Rudder? What's one of those? :confused: