Welcome to Total Immersion!
Begin with 1.0 Effort Endurance Self Coaching Course
. This series is all about stabilizing your vessel learning balance and streamline skills, and coordinating whole body movements for propulsion; learning to breathe without disrupting balance (it's easy to breathe when your vessel is stable).
Once you are stable and comfortable swimming a distance or number of laps with these new patterns of movements, vessel is stable - then move on to 2.0 Freestyle Mastery
that discuss catch, kick timing, fine tuning whole body coordination and expert breathing.
Even if you have been swimming for some time, start with 1.0 Effortless Endurance to discover and fix balance flaws in your vessel and stroke. I have worked with many experienced swimmers - competitive, masters, age-group, triathletes and fitness swimmers that have been swimming for years being unaware they had any balance issues. The human body has creative ways of adapting to imbalance that are added movements which only increase drag profile and the added workload to overcome it.
Anyway, start with the 1.0 series and you will be on your way.
Enjoy your journey!