Swimmers have to learn as many different swimming techniques as possible, as each one will put their body in a different position and use different muscles. This can be especially important if they ever need to swim for long distance as it can prevent fatigue.
The breaststroke uses a frog kick, where you will bend your knees and then kick your feet under the water. The movement of your hands will look like wiping your chest and then wiping it back in your chest. It is the slowest of the four types.
In this style you are lying back on the water. You must keep yourself horizontal as you move through the water, which you will achieve with kicking your feet.
In the butterfly style you have to bring both hands to your head at once and push them into the water to propel yourself. It also uses a dolphin-type kick, which means your legs will stay straight and as you kick them in the water.
It is probably the most popular type of swimming and provides the highest speed. In the freestyle, you are called to strike strongly with your feet while you bring your hands over your head and into the water one by one at a time. You must keep your body as straight as possible, as any sideways movement will slow you down.