It is only for Kraken.
You can either go to a Kiosk in the park or, once you are in the park, you can use an app on your phone, and get a return time for the ride. How long this is from when you get your reservation completely depends on how busy the park and Kraken is. You then return at that time, present the pass or your phone to the staff, and they will let you into the line. It would be similar to a Fast Pass, except it is only for this one ride.
Note that this does not mean you will walk immediately onto the ride. There is still a small wait time, should be no more then 10 to 15 minutes although if there are technical issues or if weather has delayed things it might be longer.