When flameworking, you hold a rod of glass (in your bare hands!) over a torch to melt it, and then use tools to shape the glass to your liking.

For marbles, you first use a marble mold to shape a hemisphere on the end of a rod, then connect a second rod to the hemisphere, melt off the first rod, and reshape the other half of the marble. You continue this process of connecting, disconnecting, and shaping the marbles until you get a round marble, and then you can break off the final rod.