I've used it in wine - not sure just why you'd need to use it in beer. You dissolve a teaspoon per gallon in a small siphoned amount of your brew when you rack to secondary and gently stir it back in. It helps to clarify as you say. It won't clear pectin/starch hazes though.
Cheyco, Sterilize the bentonite if need be, and just stir about a couple teaspoons into the primary, in some warm water, before you add your wort, then give it all a good stir.
I used some in my APA and it cleared it up nicely and eliminated chill haze to boot. I put some 180 degree water in a sterilized blender and SLOWLY added 2 tsp bentonite to the blending water. It must be in a slurry to use properly, from what I have read. Stir the slurry into the secondary AFTER fermentation has ceased and let clear for a week or two. Works pretty well.