Stars orbit each other, because if two equal mass objects are in space, then they both orbit the center of mass of the total system.

Stars orbit because of gravity - stars have mass, so exert gravity on other stars, just as the planets orbit the sun (which is, after all, a star). The galaxy also has a large black hole in the center that the stars also orbit because of its gravity. Finally, there is something called "dark matter" - matter that exerts gravity like other mass and makes up about 90% of the matter of the galaxies in the universe, but we have no idea what it is.

Good question! Stars, and other bodies in the universe, orbit each other because of gravitational attraction and conservation of angular momentum. The physical law of conservation of momentum basically says that once something is spinning, it will continue to spin (forever if nothing interferes). Because the bodies in the early universe were spinning, they continue to spin. The orbits of bodies in the universe is sort of a balance between gravity and momentum. If a star did not “feel” the gravity of another star that is was orbiting, it would “fling” off into space. Conversely, if momentum was not conserved, the two stars would collapse onto one another due to gravity. The balance of gravity and angular momentum results in circular or elliptical orbits.

Stars orbit each other because they exert gravity on each other. Anything with mass exerts a gravitational pull on its surroundings, so the starts are attracted to each other, leading to their orbiting.