It’s common to see small bubbles under freshly-installed tint. Normally, these bubbles should go away within a couple of weeks and should be very small. They may take longer to go away in cold weather and vanish faster in heat. If you have larger bubbles or bubbles that have formed in older tint, then they will not go away. You can get rid of bubbles that are causing problems by carefully pricking them with a pin or sewing needle and then smoothing a credit card over the bubble to make it disappear.
Excessive bubbling is probably a sign that your tint needs to be redone. If you are trying to install your own tint and have repeated problems with bubbles, it is probably time to go to a professional who has more experience applying the film evenly.