Eyepieces come in named designs, and the names describe how many lens elements are used and how they are arranged. The differences are real but smaller than the marketing suggests, and one design covers most people's needs for most of their observing life.
The plossl, which is the sensible default
Four elements in two pairs, a fifty degree apparent field, sharp across most of it, and inexpensive. It is the design most eyepiece sets are built from and the one to buy if you are unsure. Its weakness is eye relief at short focal lengths: a 6mm plossl has a tiny gap behind the glass and is uncomfortable, especially over spectacles.
Wide field designs
Six elements and up, apparent fields of sixty to a hundred degrees, and the sensation of looking through a window rather than a tube. They are heavier, far more expensive, and they genuinely change the experience of observing large objects. They also correct better in fast telescopes, where cheap eyepieces struggle at the edges.
Zoom eyepieces
One eyepiece covering a range, typically 8mm to 24mm. Convenient, especially for public viewing where changing eyepieces in the dark is a nuisance, and optically a compromise: narrower fields at the long end and slightly softer than a fixed eyepiece of the same focal length. A good zoom beats a poor set of fixed eyepieces.
Questions people ask about eyepiece
What is a plossl eyepiece?
A four element design with a fifty degree apparent field, sharp and inexpensive, and the standard general purpose eyepiece.
Are zoom eyepieces any good?
Convenient and slightly compromised. A good zoom beats a poor set of fixed eyepieces and loses to a good one.
What is an eyepiece lens?
The optic you look into, which magnifies the image the telescope forms. Its focal length sets the magnification you get in a given instrument.