When practicing gear changes, always ensure the car engine is off and the vehicle is secured by the parking brake. To find neutral, fully depress the clutch pedal and on the gear stick, find the gap halfway between 3rd and 4th gear.
When in neutral, the gear stick will sweep all the way to the left (over to 1st gear) and all the way to the right (over to 5th, or on some cars, 6th gear). Compare this to when a gear has been selected and there will be very little left and right movement in the gear stick. When you’ve finished practicing, leave the gear stick in neutral.