Learn to swim
You will be happier in water when you are certain not to "sink to the bottom" . Once you understand and have felt the water hold you up and realise how good it feels to be held, only then will you be able to learn to swim. How long will it take to learn to swim ? You will progress as soon as you accept to focus on yourself and your feelings, and not on the mechanics and the technical movements of swimming which you feel are still not working.
To not know how to swim is a temporary ignorance. It is possible to learn at any age ; sign up for group lessons to stimulate your learning. It is a good idea to learn different strokes, this enables you to manage your breathing, and works different muscle groups.
Learn to breathe in out of the water and breathe out in the water. And vary the length and the flow of breathing. Remember that slow movements act better in water. Breast stroke is ideal for toning the pects and arm muscles. Back crawl is often reccommended for those with back problems. Front crawl, which is often the fastest stroke, requires synchronised respiration and arm movement. The Butterfly requires both energy and great coordination of the whole body.
People who have a temperature, certain skin conditions, recent fractures, a lung infection or post phlebitis should refrain from attending pool sessions.