I have swollen gums & my gums are really tender & they look like they aren't attached to my teeth anymore , what is this ?

Needs evaluation: You gingival tissues are apparently inflamed. At a very minimum, you have gingivitis. If this continues untreated, it can turn into periodontitis. Not sure if you're actually 16 years old or not, but either way you need to be seen by a dentist to be treated.

See a dentist: Swollen gums can be a sign that you are at risk for, or already have, gum disease. Untreated gingivitis can advance to periodontitis and can eventually lead to the gap between the teeth, tooth loss and other health problems. See your dentist ASAP because the sooner you treat it the better the outcome.

Periodontitis: A gum infection. You need to have your teeth professionally cleaned by a dentist/hygienist to stop the swelling and bleeding and the gums reattach to the teeth.