Menus are sometimes hierarchically organized, allowing navigation through different levels of the menu structure. Selecting a menu entry with an arrow will expand it, showing a second menu (the sub-menu) with options related to the selected entry.
Torsion springs are normally mounted horizontally above the opening of your garage door. When you pull the door down, cables attached to the bottom corners actually force the springs to wind up, in turn energizing the system.
How do self-closing door mechanisms work? As the door is opened the arm is pulled along, expanding either the spring or the piston. On release, the spring or piston returns to its natural state, pulling the arm and the door along with them, closing the door again and exerting enough pressure to keep it closed.