Although concrete and cement are terms often used interchangeably, cement is a component of concrete and is used to bind the material together.
Cement is constructed from combining silica sand, shells, clay and limestone, which are crushed into a fine powder-like material (clinker), and then heated to approximately 2700F. The material is hydraulic, and the addition of water activates the materials, creating a thick paste which hardens and solidifies.
Cement is added to concrete to bond the aggregates (sand and gravel) together. When the material hardens, it forms a greyish stone-like structure which can be moulded to built dams, bridges and skyscrapers.