sockets

i guess you are asking the syntax to functions to make a basic server, to do this you need to use listen() first and then accept()
their prototypes are
#include <sys/socket.h>
int listen(int sockfd, int backlog);
int accept(int sockfd, void *addr, int *addrlen);

the sequence of system calls you will do is
socket();
bind();
listen();
accept();

i hope you do know how to use socket() and bind() if not google it up or refer a good networking programming book cause you will have to take care of specifing addresses in host-byte order or network-byte order. There is a good guide to network programming on the net too, <a href="https://beej.us/guide/bgnet/" target="_blank" rel="nofollow noopener noreferrer">Beej's Guide to Network Programming</a> , is short and concise. check it out. Also the above details is for gcc.

usually the socket is blocking unless you set it otherwise with ioctl