What is the heat gun for and can you briefly describe it? Do I need to use plastic rods as consumables?

Hot air guns are generally used to heat up plastic to hold various parts in place; plastic rods are generally used as consumables.

There is another kind of hot air gun is specialized in blowing hot air, used to seal the fixed parts, such as the parts on the plastic tube, blowing hot air to make the plastic tube contracted by the heat, the parts will be fixed, or sealed.