During the meeting with Uncle Kenny at the start of the mission, he tells you the problem. Some shopkeeper has been complaining about "not enough protection" and Kenny wants to show that his protection is enough. He tells Huang to destroy some cars at the Spanish Lords car lot and torch down a shop. But first, he tells Huang to get some Molotov Cocktails.
It's easy to get them. You are told to get to the nearest RON petrol station to make them. There is a choice of quater tank for $100, half tank for $150 or full for $200. You are told to fill a full fuel tank's worth of Molotovs which are, for this time, free. Drag the fuel pump into the bottles and insert a rag to make one. Continue that until you run out of fuel (you possibly end up with 10-19, depending on skill and the console you are playing on, but that's enough)
Once you got them, head over to the Spanish Lords Car Lot first. Jump over the closed gate and set the cars on fire. Then, burn down the store nearby. The more you throw, the faster it'll burn down. If you run out, you can pick up a few nearby. Destroy the two firetrucks will try to put the fire out or pull out the driver, and get the firetruck out of the way. Once the store's torched into flames, the mission is complete.