The incubation period comes after the inoculation. During this period you give the spores the time to germinate and the substrate will grow with the mycelium.
Mycelium grows best under warm circumstances. Place the substrate therefore in a warm space. The mycelium of most mushrooms grows best at a temperature of about 28 - 30 degrees C.
On small scale cultivation a closet over the refrigerator is a good place. The refrigerator is warm on the backside and this warmth increases. On a larger scale you must get a thermostat or another warming system.
However keep in mind that the substrate with mycelium also produces its own warmth. Besides the warmth the incubation space must be completely in the dark. A dark place fastens the growing pace. Light can also cause premature growth of the mushrooms.