Use the verb disembark to describe leaving a ship, airplane or other type of vehicle, like making sure you haven't left anything in the plane's overhead compartment before you disembark.
Embark means "putting passengers in a plane or on a boat." Disembark is its opposite. When you disembark, you leave a ship or a plane, like when you can't wait to disembark at the port in order to go sight-seeing. When you disembark, there is a transition — you walk down a gangplank to go from water to land or down a special corridor to get from the runway to the airport terminal — unlike when you get out of a car. That's why you wouldn't use disembark for getting out of a car.