Binoculars are a very useful piece of equipment for the astronomer. They provide great wide field images at low magnification and allow you to learn to find your way around the stars much more easily than with higher magnification telescopes.
Binoculars are, as the word suggests, two oculars or two eyepieces. A binocular is really two refracting telescopes fitted together so that you can use both eyes to look at distant objects at the same time. Binoculars incorporate a number of prisms for three purposes: Firstly, to put the picture upright again (because binoculars are usually used for terrestrial viewing). Secondly, the prisms are used to reduce the length of the tubes in order to make them easier to handle. Lastly, the prisms make it possible to reduce the width between the eyepieces in order to be able to look through them with both eyes.
Binoculars usually do not allow you to interchange eyepieces. They don't normally incorporate a mount either, although some of the larger apertures may be fitted with photo tripod adapters. Big binos are heavy and difficult to hold up to your eyes for long periods.