Hi, X-plane 11 is a complex simulator. You will not have the best experience with keyboard and mouse, but it can work.
You can find most of the answers in the manual :
http://www.x-plane.com/support/manuals/
You can change the keyboard assignements in X-plane settings, for throttle increase, decrease etc.. the searchbox in the key assignement page is very useful.
If you have no joystick plugged in, X-plane will display a very thin cross at the center of the screen. Clicking on it will activate the "mouse joystick mode". That should help you get started.
Welcome to the platform!