There are a lot more sensors in a car, but these are the main ones that play a role in the ECU providing the right amount of fuel for every occasion in the engine.

The mass airflow sensor lets the ECU know how dense the air is that is entering the engine

The oxygen sensors are aware of how much oxygen is in the exhaust. This helps the ECU to determine whether the air fuel ratio is too lean or too rich so it can make adjustments to make the ratio perfect.

The throttle position sensor monitors how much the throttle is being depressed which effects how much air is entering the engine. The ECU uses this information and rapidly increases or decreases the amount of fuel being sprayed by the injectors.

The coolant temperature sensor tells the ECU the temperature of the engine.

The Voltage sensor keeps track of the amount of voltage in the car so the ECU can raise the idle speed if voltage is dropping. This keeps the car from stalling.

The manifold absolute pressure sensor monitors the pressure of the air in the intake manifold. The amount of air that the engine is drawing in indicates how much power the engine  is producing. The more air the engine draws in, the lower the manifold pressure. Basically, the sensor is used to see how much power the engine is making. 

As the name suggests, the engine speed sensor monitors speed.