Each line in /etc/fstab contains infomaton on one filesystem. For example,

/dev/hda7    /    ext3    defaults    0 0

There are 6 fields:

1. device name (e.g., /dev/hda)
2. mount point
3. filesysem type (ext2, reiser, iso9660, etc.)
4. options (ro, noauto, user, usrquota)
5. dump should backup this filesystem (0=no, 1=yes)
6. fsck order on reboots (0=dont check, 1=root filesystem, 2=other filesystems)