Complex sentence: Yogi makes his way to the cockpit and proceeds to press buttons in an attempt to open a door; it isn't until he presses the last button that the Spruce Goose's engines begin to light up and magically turn on.
Split into simpler sentences: Yogi makes his way to the cockpit and proceeds to press buttons in an attempt to open a door. It isn't until he presses the last button that the Spruce Goose's engines begin to light up and magically turn on.