/sbin holds system administration binaries: tools used to manage the machine that are typically run as root. The distinction from /bin is intent: /bin contains tools any user might need (ls, cat, cp), while /sbin contains tools for system configuration and maintenance (mount, fsck, iptables, ip, init). In practice many /sbin tools can be read and sometimes executed by non-root users; the separation is conventional rather than enforced by permissions.

/sbin/init          PID 1: the first process started by the kernel (or a symlink to systemd)
/sbin/mount         mount filesystems
/sbin/umount        unmount filesystems
/sbin/fsck          check and repair filesystems
/sbin/mkfs          create a filesystem on a block device
/sbin/ip            configure network interfaces, routes, tunnels
/sbin/iptables      configure the kernel packet filter (legacy; nftables is the successor)
/sbin/fdisk         partition table editor
/sbin/modprobe      load kernel modules and their dependencies
/sbin/shutdown      halt or reboot the system cleanly

Like /bin and /lib, /sbin is a symbolic link to /usr/sbin on distributions that have adopted the merged /usr layout. On such systems ls -la /sbin shows sbin -> usr/sbin.