I have a box centered on the origin of the scene. I want to grab the bottom right edge and pull it in towards the center to taper. I want to do this on the left side too, and I want to be able to translate that edge precisely using some kind of number input, so that I can control exactly how far it goes, and replicate it on both sides perfectly. I know that I can probably do something similar using mirror mode, but I'd like to know how to do this for more than just this, as it would help me to be more accurate when I'm box modeling.
To Translate any selected Vertices, objects or edges you press G and then after that depending on what axis you want to move it on you press the corresponding letter, which can be Y,X, or Z.
Secondly, you can either move it yourself with your mouse or type in a number. You can use numbers with decimals and or negative numbers which will translate in the opposite direction.
As for getting the edge to where you want it to be you will have to experiment with numbers. Hope this helps, and good luck.