How to take close-up photos (20 to 50 cm distance) with Nikon D5200 camera, and how to set them up?

There is no special setting. Common sense holds that only the setting is high resolution, accurate focusing, using a small aperture (long depth of field), and shooting with a short focal end when the imaging size of the subject is appropriate.

However, in any case, accurate focusing is a prerequisite. The depth of field of large aperture shooting is short, and the short distance before and after the focus of the main object is also very clear, which is also a common means. Many macro shots are also shot in this way. I think this may be what you call sharp. Of course, the telephoto end can also be used.

For example, this is normal, close-up shooting, and the aperture is not set very small.

Therefore, the focus must be accurate, and the aperture size and lens focal length should be set appropriately according to the scene.