To move forward, a sailboat must balance the pressure of the water on the hull with the pressure of the wind on the sails. To achieve this balance, the sailor adjusts (or trims) the sails depending on how the boat is orientated with respect to the wind. With the proper sail trim, a sailboat can sail in every direction with the exception of directly into the wind.
The first thing to know when you are out on the water is what direction the wind is blowing. Once you have determined where the wind is coming from, you can begin to adjust your sails. In general, the closer you are sailing to the direction the wind is coming from, the tighter in you want your sails. When you are sailing away from the wind, you should let your sails all the way out to best catch the wind. Listed below are the most common points of sails.
In Irons - the boat is pointed into the wind and the sails are luffing. The boat is not moving through the water.
Close Hauled - the boat is sailing as close to the wind as it can without its sails luffing. The sails are pulled in tight to the center of the boat.
Beam Reach - The boat is sailing perpendicular to the wind with the wind coming over the side of the boat. The sails are positioned halfway in and halfway out.
Broad Reach - The boat is sailing with the wind coming over the quarter and the sails are let most of the way out.
Running - The boat is headed directly away from the wind with the wind coming over the stern. The sails are positioned all the way out. On this point of sail it is possible to sail wing and wing, with the main sail on one side of the boat and the jib sail on the other side of the boat.