Do not know where to start with the swim portion

Welcome to BT and congrats on your quest to become a triathlete! It is many an injured runner who has become a joyful triathlete

Take swimming lessons at your local YMCA (or equivalent). They will be able to recommend which level to start out at. Whether you take individual or group lessons, you will gain great confidence in learning proper strokes and how to move through the water. 

Swimming is an interesting mix of comfort in the water, body position, technique, and work. That having been said, I have yet to meet the individual who cannot master swimming.

Everyone starts with a certain level of comfort in the water. The more comfortable you are with your face in the water the better things will go. If you tense up when you are in the water, you will become less buoyant, and have to work harder. The more time you spend in the water, the more at ease you will become.

When you are in the water, your body acts like the two arms of a scale. When you raise your head on one side, your feet will sink on the other side. This is where body position comes into play. When your feet are down you will produce more drag, and have to work harder to move through the water. If you can maintain a level position, and cut through the water like a torpedo, you will produce less drag, and move very efficiently through the water.

There is a lot of subtle technique in swimming. A good flutter kick, not dragging your hands on the catch phase, lengthening the stroke are just a few examples. The best bet to learn the best techniques for you, is to get with a masters group or a good coach. A coach can analyze your specific stroke, and introduce the specific technique and drills that will help you become the most efficient at moving through the water.

The final element is simply putting in the work. Just like the run and the bike you have to put the mileage in. Start at 500 yards and keep adding 50 to 100 yards additional to each workout. Work toward being comfortable swimming 2X the distance of the event you are training for.

Be confident, you can swim.

Cheers

Body fat doesn't mean your a sinker or not.  The swim portion is usually the part that most people get hung up on, so your not alone.  There are a million things to be done, which sometimes is the problem.  Here is my 2 cents.... Be patient!  It may take months or longer to learn how to swim.  Then it may take many months or longer to get efficient at it.  Then it may take many months or longer to get fast.  I would highly recommend getting the Total Immersion-Freestyle Made Easy video.  It is a real good way to get you doing laps in a pool.

By the way.  13 months ago I couldn't swim 50 yards at all.  And I know that SS Minnow was having issues last year too but now she is kicking butt.  Be patient.  You can do it, but it won't be easy.

+1 on the coach.  find someone you are comfortable with as it will take a number of lessons to get the basics down.  It will no doubt be an investment on your part, but it sounds like Triathlon would be a good sport for you that you would really enjoy and succeed at.  My sister hired a coach who was a competative high school swimmer.  Great swimmer:  terrible coach.  So just know that not all good swimmers make good coaches, so don't be afraid to change up instructors if need be.  (ie:  don't worry about hurt feelings)

good luck