When you sign up for an NBCUniversal profile, you receive a one-time grant of three credits. Each credit allows you to access one locked episode of an NBC TV show. Credits do not work for live streaming. Credits do not expire. Once a credit is redeemed for a given episode, that episode should remain available to you on all your devices, as long as you've signed in with your NBC profile.
To check how many credits you have remaining, click on any locked episode. You will be offered the option to use a credit, and your balance will be displayed on the confirmation screen.
Additional credits are not available at this time except when they are offered in certain promotions or other special circumstances.