I'm so glad Williams started carrying these. Depending on your recipe, add one 3# can or two to a 5 gallon batch of beer. When the fermentation slows, add a can to the primary fermenter. If adding a second can, wait until the fermentation slows again. After adding fruit, the fermentation can be quite vigorous so be wary of a clogged airlock.
I've added red raspberry puree to William's Honey Wheat kit and it turned out pretty well.