A sailboat will have one or more sails affixed by lines to other parts of the boat, usually to a mast (a vertical pole) and/or boom (a horizontal pole) but also to lines routed to winches (mechanical winding devices) or cleats (fixed fittings for tying). Operating these devices in order to manipulate the position, shape and size of the sail(s) in relationship to the direction of the wind is called "trimming the sails."
If a sailboat were to rely solely on the force of wind upon the sails for direction of movement, then the direction of movement would forever be the same as the wind. When a sailboat moves in the same direction the wind is blowing or at slight variations to it, it is termed as "running before the wind" or "running." However, when a sailboat must sail to some degree into the wind, it is called "beating," "tacking," or "heading up" and must utilize the added dynamic of a keel or centerboard.
Keels and centerboards are sturdy underwater extensions protruding from the bottom center of the sailboat. The keel is a fixed extension and is usually found on larger sailboats. A centerboard, sometimes called a "dagger board," can either be a pivoting type or dagger type and is retractable. In each case, the extension works to force a resistance counter to the force of wind upon the sails and results in a new direction of movement. Without a keel or centerboard, the sailboat would move sideways only and likely tip or capsize.
The ship’s wheel or tiller arm (a handle in place of a wheel) connects via lines and blocks (pulleys) to the underwater rudder (steering blade) located at the rear (or stern) of the sailboat to comprise the helm, which completes the assortment of devices necessary to purposely steer and direct a sailboat through and atop the water.