They are introduced in Rubble Trouble Moscow. In the fourth level, Larry is stuck on top of a large wooden tower. When the weapon is selected, Garry will appear with a blue and purple birthday hat, pulling a trolley with two molotovs.
A line of circles (called by the game as "aiming guide") will appear, and can be used to plot where the molotov bottle will hit.
When the player has picked the position of where they want the bottle to go, clicking the mouse will cause Garry to toss a molotov bottle in that direction. When the bottle hits something, it will send out flames in many directions, as well as explosions. When the explosions hit something, they turn to flames.
Flames will ignite wood, and can travel through pieces if connected close enough. When on the wood, the flames will turn the wood black, soon causing them be destroyed. The flames can only harm wood and explosives, and so cannot destroy stone or metal.