When attempting to access a live stream or full replay, you will be prompted to select your cable, satellite or telco TV provider (e.g. Comcast, Time Warner, DirecTV, AT&T) from a list. You then will be asked to verify your TV subscription, this often means only entering the username/password corresponding to the online account you established with your provider.
Head to the App Store for the NBC Olympics Live Extra iPad App. The Olympics don't start for another couple weeks, but you can watch footage from the 2008 Beijing Olympics along with 2012 Olympic Trial highlights until then.