Overhead garage doors, whether they roll up in sections or swing up in one piece, operate on spring tension. The door moves on metal tracks on the garage walls, and a heavy spring or springs provide the power.
Lubricate the chain or the screw on your opener annually with white lithium grease. Spray-on versions are available at most home centers. Lubrication will make the opener's operation smoother, quieter and extend the life of both chain and opener.