"Put the clutch in" - not sure what you mean.
If you mean when you press the pedal, disengaging the clutch, then you're supposed to take your foot off the throttle as well
If you mean when you take your foot *off* the pedal, engaging the clutch and connecting the engine to the roadwheels, then it's clutch slip. You're supposed to match the engine speed to the roadspeed/gear combination so that there's no jerk and no speed differential for the clutch to take up - changing clutch plates is expensive. With a bit of practice you can change gear without using the clutch at all, though it's not to be recommended.