What do SLR P, S, A and M mean? How to use these well?

P file is program automatic, you can manually set ISOS file as shutter priority, you can manually set shutter, aperture is automatic, A file is aperture priority, you can manually design aperture value, shutter is automatic, M file is manual file, and you need to manually set aperture shutter when shooting moving objects. In order to avoid blurring, the S-file is usually used to set a higher shutter, and the aperture allows the system to automatically adjust when shooting people, so as to obtain a better background blur effect. Generally, a file is used to manually set a larger aperture value, and the shutter allows the system to automatically set M file. Generally, you will be familiar with it after you have a certain photographic technology foundation, and you need more experience to use M-files.