Gas cans in PUBG have a new update where you can readily use the gas by pouring the gas inside of them and using them during a match. The gas inside of them will promptly go on the ground into a dark pool, which you can light on fire to damage opponents who mistakenly walk over them.
To pour out a gas can you need to move it to your melee slot to hold it. Once you have it out, all you have to do is treat it as if it were a melee weapon and attack with it, and your character should start pouring out the can’s contents onto the ground. Most gas cans should have around seven seconds worth of gas inside that you can pour out to prepare an ambush.
Now that you have the gas on the ground, you can readily light it using a Molotov cocktail, grenade, or by shooting it with any of your weapons. You can do this from a range, giving you an excellent opportunity to wait in a nearby bush, or in an adjacent building for an enemy to walk over it. Once they cross the gas, hit it with one of those items, and you should create a firey barrier.
Unfortunately, the gas does not stay on the ground forever. It remains there for a couple of minutes, but it does eventually disappear. If you plan to use it, you cannot wait forever for someone to run across it. You may want to pour the gas out right before a blue circle completes, or on one of the chokepoints to the next portion of your PUBG match.