Eyepieces are multi-lens components that allow you to achieve different magnifications with your telescope. You cannot start observing with just a telescope and no eyepieces.

The shorter the focal length of the eyepiece, the higher magnifications it produces. It makes sense to have eyepieces in a range of focal lengths, preferably a reasonable selection which takes you in even steps from low to high magnification - to equip you for all the different types of observing and astronomical objects.