Masters is really just a swim team for adults. There is a national organization with a website that can help you find practices in your area as well as swim meets, ets-http://www.usms.org.
I am officially the slowest swimmer at our practice, but everyone including the coach is very supportive. I only really learned to swim 4 years ago for triathlons and I am still learning. My biggest accomplishment lately is breathing on both sides. We are still working on little things like butterfly & breast-I am just not coordinated enough. DH is a swimmer, which is why I started, and his theory is that the better all around swimmer you are, the easier your tri swims will be.