I am considering going scuba diving, which I know is where you can dive underwater and explore gorgeous marine life and still be able to breathe by using a breathing apparatus, but it scares me. Have you been?
I have never been fully scuba diving but I have been snorkeling  in the Bahamas. I would love to go scuba diving though
I know scuba divers often use breathing gas, which lets them more freedom than surface divers, as well as longer endurance. So, I can just imagine how much more you can see under there!
I think it would be amazing to look at all the creatures we can't see from up here. I would also be concerned about using the air tank but I think if you practiced it would be ok. 
Yes, I know certain scuba setups sends the exhaled gas into the environment. But, I think they often have more than one cylinder so that would be reassuring too, knowing you don't have to worry about not having ample oxygen!
Exactly! At the same time having more would weigh you down.  I guess the professionals know what they are doing and would set you up correctly. I would want to dive with a professional for sure.
cylinder or cylinders may be used for an equivalent dive duration. Rebreathers extend the time spent underwater compared to open circuit for the same gas consumption; they produce fewer bubbles and less noise than open circuit scuba which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.
Scuba diving may be done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving
refers to a vehicle that may or may not be enclosed, but in either case water floods the interior so SCUBA equipment is used to facilitate breathing. In both single atmosphere and ambient pressure subs, there is no need to use SCUBA equipment and occupants can breathe normally without wearing any equipment.
Deep-diving manned submersibles.
Some submersibles have been able to dive to great depths. The Bathyscaphe Trieste was the first to reach the deepest part of the ocean, nearly 11 km (7 mi) below