Well modern glitter is made from plastic. It starts out as a large plastic sheet which has been extruded from melted plastic pellets. It is usually covered with a layer of foil which is what gives it that shine that everybody loves. Once the plastic sheet has been formed, it's cut into tiny pieces until it looks like stardust. This process is obviously done by a machine though.
Hexagonal or square pieces are common but there are other shapes as well. The entire process can simply be simplified into feeding the foil-plastic sheet into the machine and having it cut it into the desired shape.
The resulting pieces of glitter are then packaged into final products, and this depends on what the customer wants. It could be a bag of glitter, hair spray formulation, make up etc.