Clear glass (Cullet) is melted, then minerals are added to get the color. This is all done in a crucible that is in a very hot kiln or oven.
After 4-14 days of mixing and off-gassing the color is done.
To pull rods they simply pull the glass from the molten color as a steady pace to get the proper size
To pull tubing, they use a metal tube, stick it in the glass and pull while blowing in air.
There are also other ways that smaller artists can do this, and extra-large glass facilities use machines to pull.