Here is a great video to help you understand the tongue, its importance, and how it affects airway, as well as why nasal breathing is so important.
Here is the website for the ear/nose/throat doctor, Dr. Soroush Zaghi, who is at the forefront of educating people in the medical field on tongue ties. You'll see on the front page of the website that he has a video of testimonials of his patients that have had their tongue-ties released.
Here's another video that sums up tongue position and its effects on the developing jaws.
Here's a short video that talks about what a tongue-tie is.
Here's a short video on the connection between tongue-ties and mouth breathing.
Here's a short video that describes a posterior tongue tie.