In the beginning, gas powered vehicles used a carburetor to get gas into the engine. This worked well, but when fuel injection came along, things changed quickly. Fuel injection, especially electronic fuel injection produces fewer emissions and greatly increases gas mileage.
The carburetor was an ingenious invention in itself. Your car's engine has 4 cycles, and one of them is a "suck" cycle. Put simply, the engine sucks (creates extreme vacuum inside the cylinder) and when it does, the carburetor was there to let the right amount of gas and air get sucked into the engine. While great, this system lacked the precision of a pressurized injection system.
Enter fuel injection. Your engine still sucks, but instead of relying on the suck, fuel injection shoots exactly the right amount of fuel into the chamber. Fuel injection systems have gone through a few evolutions, adding electronics was a big step, but the idea has remained the same: an electrically activated valve (the injector) spraying a metered amount of fuel into your engine.