Fuel
Vehicles have limited fuel. When your vehicle runs out of fuel, you are in big trouble.
Gasoline
To refuel most normal cars and bikes, you simply go to a gas station, marked by a jerrycan icon on the map.
To put gasoline, park your car at the pump first, then open the gas station menu, and then select Vehicle to start pumping gasoline.
Keep in mind that gas stations don't take cash, and you must pay directly from your bank account balance instead.
Electric Vehicles
For EVs the process is similar as before, but you use EV chargers instead. They are located in the parking area of almost all gas stations.
Don't be like this woman who tried to put gasoline in her electric car!
Planes and Helis
To refuel an aircraft, you must park it at a designated parking area instead. These areas will have a "Ground Services" menu that can be opened by pressing G.
Using a Jerrycan
You can also use a jerrycan to refuel cars and bikes.
Buy one at any convenience or hardware store, then fill it with gasoline at any gas station by selecting "Jerrycan".
To refuel a vehicle, stand near its tank and hold left mouse button to refuel it.