Yes, to tare a scale is to return it to zero. You place the cup on the scale, then use the tare function to set it to zero, so the weight of the cup is excluded and the measurement is only of that which you put in it.
I find that when weighing charges, I have to empty the cup, place the cup on the scale, wait for it to settle (a few seconds), hit the tare button to return it to zero (Mine is usually off by -.2 to -.4) and then weigh my next charge. I have an RCBS 505 that I used to test the consistency of the electronic scale and if I go through this routine, it does provide a very consistent measure. I guess it was just disappointing to me that the electronic one provided little or no speed advantage compared to the manual variety.