Go by RPM; for each bike this is different, but should be in the 2000 to 4000 RPM range. You don't need a gauge, just go by sound. If the engine is whining, you're too high on the RPM range.
Put it in neutral, that will disengage the clutch from the motor. And don't ever put it in park (P) when the car is moving, because that will lock the...
While the car is in motion, take your foot off of the gas pedal, press the clutch, and change your gear. Then, gradually take your foot off of the clutch...
While your vehicle is in motion, lift off of the gas pedal and slowly press down on the clutch. Use the shifter to switch into the next gear up. Slowly...