Breathing techniques are for increasing breath hold, learning to breathe properly, reducing anxiety, eliciting calm, and using oxygen more efficiently.

Give yourself a background in swimming. I only swam once in a summer league when I started training, but I spent 8 months prior to joining just being in the pool everyday and swimming up to 5000m at a time. Start off doing what you can and then work your way up. It is a matter of consistency and technique.