Mowing your lawn is a required chore. Most lawn mowers today use a combustion engine. As such, you will need to put gasoline in the mower before it will run. Refer to the owner's manual that came with your lawn mower to determine what kind of fuel your lawn mower should use. Some lawn mowers require gasoline with a higher octane, while others may not. There are even lawn mowers that require diesel fuel.
Locate the gas tank on your lawn mower. The gas tank will look like a plastic jug sitting on the top, front or side of the engine. Some mowers, however, will have the gas tank covered up, as with the rest of the engine. If this is the case, skip this step and move on to step 2.
Search for the gasoline receptacle. This will be covered with a black cap, with a symbol signifying gasoline on the top. This symbol can vary by lawn mower, but will usually either say "Gas" or have a little picture of a gas pump on it.
Remove the gas cap. Most lawn mowers use a threaded cap, which you can twist right off of the top. Some other common types of gas caps include lock caps that require a key, or a cap that is fastened down on the bottom by a keyed locking mechanism. These you can just turn until the opening key point matches up, and lift it right off.
Place a funnel in the gas receptacle. A funnel is not necessary if your gas can has a pouring nozzle built into it. If it doesn't however, a nozzle will help you get all of the gas from the can into the tank without much spilling.
Pour the gas from the gas can slowly into the gas receptacle. If you are using a funnel, do not pour it too fast. The neck of the funnel will only allow so much gasoline through at one time. If you pour too slowly, you will end up spilling some gas over the side of the funnel. If your gas can has a pouring nozzle, you can pour as fast as you want, as the pour nozzle will regulate the speed at which it comes out. You will be able to see the gas level in the tank as you fill it up. Make sure that you stop pouring before it gets too full. When you have enough gas, remove the gas can pour spout or funnel from the gas receptacle.
Replace the gas cap, and screw it on tightly.