If you talk about reducing to the essentials when swimming, then you can't avoid the topics of water position, arm stroke, breathing and recovery. We have briefly described what needs to be considered in each case and which exercise helps best.
water position and glide
In each of our swimming seminars, we "buzz around" on this topic. The most important thing when swimming is the position in the water. The body should lie as flat as possible on the water surface. In this way you reduce your cross-section in the direction of swimming and have the smallest possible water resistance. In order to achieve a good position in the water, good trunk stability and a good leg kick are necessary. Only those who are in a good position in the water can glide optimally and swim quickly. These two skills go hand in hand when it comes to swimming.
Exercise: Every workout includes 200-400m leg kicks. The prone position can be alternated with side and back positions. Every athlete should train their core muscles 2-3 times a week for about 30 minutes.
Once you've got your position in the water under control, the next thing you should do is work on your (underwater) arm pull, because the arm pull gives you the propulsion you need for swimming. Here, too, the first step is gliding, followed by catching water, the pulling and pushing phases. Make sure that you don't overload your shoulders with a stretched arm pull and ensure optimal propulsion with a dynamic push-off in the pressure phase.
Exercise: The best exercises for the arm pull are unilateral arm pulls, as well as the classic "skulling" exercises. Board and fins are good tools to focus on individual facets.
Swimming is a cyclic movement. This means that the exercise takes place under water, the above water part is (actually) the recovery phase to get fit again for the next move. So if you tense your arms and shoulders as much as possible both above and below the water, you will not have a recovery phase and will be flattened out pretty quickly.
This means that the arm must be guided forward as loosely as possible (elbow high) over water and the muscles then get a well-deserved break before the next arm pull.
Exercise: Stretching and strength training for the upper back help to make the shoulder area more flexible. In technique training, zips and water loops are good exercises to increase the looseness when retrieving the arm.
Nothing works without oxygen...so we just have to breathe at some point in order to (live and) be able to move on. As banal as it sounds: As a freestyle swimmer you have to breathe out of the water and inhale over the water. To get to the point even more precisely. If you haven't finished exhaling, but you are already turning your head sideways to breathe, you will have a timing problem, because then there will not be enough time to inhale enough.
Exercise: Here you can do an exercise with a board, to exhale under water until your lungs are completely empty. Only then does an arm pull with breathing follow. Then the exercise starts all over again.