How does socket_select really work?

Hello, I took some time to study sockets in php. I already use the ratchet at one time but I was interested in using the sockets without a library, just to get more knowledge, but with that came a doubt that I can not solve it, I've researched everywhere and the explanations are always not very clear, the socket_select () function does exactly what? How could I detect new clients connected with it? I know that it is widely used for multi connections, however, I do not quite understand its application. When I pass the array $ read in the first parameter socket_select ($ read, ...) would I get new clients every loop if it exists?