Sheet goods are sized and fitted to create the "box" which consists of sides, back and bottom with or without a toe kick.
Lower boxes in kitchens are generally 24-inch deep and 34 3/4-inches tall to allow for a 36" finished top. They are used to store the bulkier and heavier kitchen items and may be configured with any combination of drawers and doors, including pull-out systems for easier access.
Upper boxes in kitchens are generally 12-inch deep and 18" above the counter top to allow for a working area below. They are used to store glassware, dishes and dry goods and generally configured with adjustable shelves.
The type of box construction will determine the structural integrity and long-term usability.
Traditional or "face frame" cabinets are built with an integral frame on the finished face, providing additional strength, especially over long runs.
European or "frameless" cabinets are built with edge banding on the finished face, providing a bit more space for drawers, though less strength over long runs.
Just as the names suggest, plywood is a much stronger form of sheet goods because of the cross-banded assembly. A variety of finish surfaces can be sourced with plywood making it an excellent choice for more exotic species of wood.
Particleboard describes the core of laminated finished sides, like in Ikea furniture.
MDF is medium density fiberboard, often select for its paintability, but not for structure.