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.
Type of build

Plössl

Super Wide Angle SWA

Ultra Wide Angle UWA

Extreme Wide Angle XWA

zoom eyepiece

Reticle eyepieces