There are many diseases that can't be cured, but can be kept from being lethal by supportive interventions. At its most basic level this may simply be providing a patient with shelter, food, and water while they fight off the illness. If you've never suffered from a serious illness you may not appreciate that it can weaken you so much that you may not be able to feed your self or even rise from your sick bed. It would be a shame to die of dehydration just about the time your immune system was killing off the disease.
We don't have a cure for Covid-19, so if you are infected, the only way you are going to recover is if your immune system is able to mount an effective defense to the virus. Fortunately this is a natural and inevitable process for most of us. The problem is that it takes time, so there is a race between the damage being done by the virus and the immune system's response. There are many medical interventions that can help you survive the immediate damage, and buy you more time to mount an immune response.
None of these treatments is guaranteed to save the day, but they have helped many people. Managing these treatments is complex, and may require minute by minute monitoring by skilled ICU nurses and doctors.