For adding it to keg: 1 tsp for every 5 gallons. Bloom in ~ 1 cup colder water for 15-20 minutes, then microwave for about 1:20 or so until it hits about 150F (that's what I've found with my microwave). Stir, then dump into cold beer.
I fine in the keg using this method. Just plain old unflavored Knox gelatin. I've had great success in clearing most beers. I also have used Bentonite. Follow the instructions on the package. It's a PITA to get it to completely dissolve, but it settles nicely in the bottom of the keg and stays tightly packed.
I prefer the gelatin fining though.