how do you make the plane go to the selected airport with ap

how do i get the plane go to the selected airport with out piloting manually please explain what I have to do how do you also keep the aircraft level with out making it go up or down just stay in the same altitude.

Quick and dirty answer.
Ctrl + Z sets altitude ( stops aircraft from going up and down)
Z toggels Auto Pilot

With your auto pilot set to heading your air craft will fly the heading that
is determined by your heading bug on VOR1.

Suggest you consider taking some of the training courses that come with
the program they will give you a good start.