Each half of the chip is one motor controller. The EN pins are the enable pins. If you put those to high (VCC), the motor controller is enabled. If you put those low, the motor controller is disabled. There are two for both motor controllers in the L293. The A pins are the controller pins, which control if the motor is on or not. The Y pins are the pins that go to the motor.
Go to the datasheet and look at the truth table, it should show you how different settings with the A and the EN pins will drive the motors.