How the submarine float and sink?

A submarine floats and sinks by adjusting its buoyancy through the use of ballast tanks. When the submarine wants to sink, it fills these tanks with water, increasing its weight and causing it to descend. To float, the submarine expels the water from the ballast tanks, replacing it with air, which decreases its weight and allows it to rise. This ability to control buoyancy enables submarines to navigate at various depths in the water.