They append the stuff inside the quotes to the /etc/fstab file. This in turn tells the system to automatically mount the file systems specified on the lines at boot (with default options, but read-only). It also simplifies later mounts by having the options set and which mountpoint and partition that belongs together, specified in advance.

If you had after boot unmounted the /drive0 partition, you can the mount it by simply saying "mount /drive0" instead of also having to specify the options, filesystem type and partition...