What does it mean when car shudders when in first gear with clutch all the way down?

My car shudders in first gear with the clutch down and have to rev it a bit for the shudder and noise to disappear. I know the car jolts if you are in too high a gear but surely if you are stationary waiting at traffic this shouldn't happen the car doesn't stall when still even though it's shuddering a bit. You have to rev the accellerator for the car to stop making a noise - it then goes completely silent. In reverse you have to use high revs to move the car to the point that normally you would think it's a bit too much but it's not that bad - The car stalls sometimes because I forget to do the higher revs.