I generally add gelatin to secondary after a period of conditioning (lenght of conditioning prior to cold crashing in secondary depends on the beer). I will typically soak the gelatin in cold water for an hour, boil to dissolve, cool to about 70 F, and add to my beer which I then place at 34-38 F for 5-7 days. Always works great. You can typically see it in action, and it appears as phases separating. Just don't use more than the 1.5 g/5 gallons for beer, as it can actually start stripping components of the beer that are associated with body.