The clay minerals are commonly thought of as any rock or soil material consisting of small particles that can be molded when wet. Technically, the term for them is hydrous aluminium phillosylicates. Clays are a major constituent of soils. There are many groups, such as kaolinite, montmorillonite/smectite, Illlite and chlorite. There are numerous subcategories, which is a subject unto itself.
Uses for clay run into the thousands: ceramics, fuller's earth, meerschaum, fire bricks, carbonless paper, bricks, tile, pottery, filtering, as a filler in plastics and rubber and so on.
I remember an old Girl Scouts book I had once that explained how to extract clay from soil, make it into useful objects, and fire it.