The goal here is to insert into fstab the IDs of the volumes you don't want to mount when the system boots.
You have two options. Specify the UUID (universally unique identifier) of the volume, or the volume disk label.
The volume disk label is the easiest method, because you already know it. For example the internal Macintosh hard drive is labelled "Macintosh HD" or whatever you named it. So, the line to add, looks like this
LABEL=Macintosh\040HD none hfs rw,noauto
The \040 represents the space character (see ASCII table) in octal numeral system.
The other option is to put in the UUID of the volume you don't want to mount.
To know the UUID you must issue a couple of commands.
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS MacOSX_SYS 499.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
In my example this is /dev/disk0s2.
The last command let you know the UUID associated to the volume
diskutil info /dev/disk0s2 | grep UUID
Volume UUID: 72B18CD5-ADD4-382E-A877-F67239F204B3
So, the line to add to fstab is
UUID=72B18CD5-ADD4-382E-A877-F67239F204B3 none hfs rw,noauto
Save the new fstab file and reboot.