Once plane is at desired altitude, trimmed and level…
Press AP
Press Altitude Hold
You can adjust altitude to a new level and press Flight Level Change
With correct power plane will move to new altitude. You may have to adjust Vertical Speed. Press Vertical Speed Hold and adjust VS.
Put heading bug in the direction you want to fly
Press Heading Hold
Adjusting heading bug will steer the aircraft.
Forced use of the elevators or ailerons (Yoke) or use of rudder will cancel AP