First a design is made in wax.
Then the goldsmith will mount the wax model in a flask surrounded by investment.
When the investment hardens, then the flask is put into a burnout oven and heated until the wax melts out. This leaves a hole in the investment that is exactly the size and shape of the wax design.
Then the flask is mounted in a casting machine. Gold or other metal is melted in a crucible mounted against the flask.
When it is melted to the right temperature, it is flung into the flask by centrifugal force or vacuum suction and it hardens into exactly the size and shape of the original design.