"To release the clutch" means to let go of or stop holding the clutch pedal in a vehicle, allowing the engine power to be transferred to the wheels. This action enables the vehicle to start moving smoothly. Full definition
This means that the answer to your original question is that it is ok to give exactly the right amount of gas when releasing the clutch pedal. (mechanics.stackexchange.com)
With the car stopped I shift into 1st gear and slowly release the clutch while at the same time slowly pressing the gas pedal. (mechanics.stackexchange.com)
That is why it is normal to apply gas while releasing the clutch while starting in first gear. (mechanics.stackexchange.com)