Bentonite is a negatively charged, clay-like mineral that removes positively charged particles. It works best when the wine is at warmer temperature. It is also more effective at a lower pH because the positive charge on proteins is stonger at more acidic levels.
Generic low level fining for five gallons: blend 1/2 tsp (approx 3g) with 1/2 cup of hot water (140 to 200 F) in a blender for 1-2 minutes. Let stand for 60 minutes, mix, and stir into wine. Let stand for 10-14 days and then rack off. This is fining at .16g/L
For a generic mid level addition: Follow above directions but use 9 grams of with 3/4 cup of water. This is fining at .5g/L.
When making a wine kit from concentrate you will often add the bentonite on the first day. This happens for a few reasons. It is used as a nucleation sites for the removal of CO2. Additionally, the bentonite is moved all around the wine by the CO2 and thus less can be used more efficiently in a shorter time period.
This is a Vitiben Bentonite.