Here the sailboat is sailing close hauled, or as close to the wind direction it can. Most boats can sail within about 45 to 50 degrees of the wind direction. (No boat can sail directly into the wind.) Close hauled is also called beating.
Notice that both sails are pulled in tight, and the boom is centered down the centerline of the boat. The curve of the sails is like the shape of an airplane’s wing, generating lift—a force that, in combination with the effect of the keel, results in the boat being pulled forward.
Note that the boat is also heeling (leaning) to starboard (the right side). Sailing close hauled produces more heeling than other points of sail.
When close hauled, the jib is trimmed in tight for equal airflow on both sides. See how to trim the jib using telltales.