You can’t see much through a telescope without an eyepiece. Every telescope comes with one or two of usually middling quality. Eventually, you’ll want to upgrade your eyepieces to get wider or crisper views of the Moon and planets and deep-sky objects. A good eyepiece can make a huge difference in what you can see. Eyepieces come in two sizes: 1.25″ and 2″, and a huge range of prices… from $30 to $600 or more. Some modern eyepieces like the Nagler and Ethos designs from Televue give you a wide-field view as if you are looking out a spaceship window.