A crystal is the generic term for solids, having at atomic/molecular level regular structure, what macroscopically manifests in formation of regular geometric 3D crystallic objects. The size and shape can be natural, formed by crystallization from solutions or melted solids, or mechanically broken, e.g. in production mills.
A pellet or a granule refer rather to a particular shape than to nature of the material or way of its forming. They are not particular crystal forms, but they rather relate to technology that produce them. They do not follow the natural geometric patterns of crystals and are usually polycrystallic. Solids are forced by the technological process to take a specific shape. Material of pellets/granules may not be crystalline at all.
Pellets as somewhat flatted shapes are often result of pressure binding and cutting of solid microcrystallic or amorph matter. But it could be prepared from originally liquid, or liquid+solid forms as below.
Granules as more spherical-like shapes than pellets. Granules of homogenous inorganic or organic substances are often produced by fast cooling of melted solid or by fast evaporation of hot saturated/oversaturated solutions. Alternative option is using a solidifying binder, if granules do not have homogeneous composition - e.g. like pet feed.