Each set of strips (one for the top teeth and one for the bottom) has a plastic liner that covers the gel side. Simply peel away this layer when you are ready to apply the strip to your teeth. Most teeth whitening instructions will tell you to not brush your teeth just before applying the strip. This will help them adhere to your teeth better

To apply, simply remove the teeth whitening strip from its liner and place the gel side to your teeth, aligned with your gum line. Press against your teeth for best contact and fold the remainder of the strip behind your teeth. Be sure to read the directions on the package of your Crest 3DWhitestrips pack to learn how many times a day you should wear the strips. This will vary by product and should be clearly stated in the teeth whitening instructions - some require one application, while others are meant to be worn twice a day.