The first column is the filesystem device that you wish to mount. Normally it will be something like /dev/hda1 for a physical hard drive, but can be in many other forms. For example, to access a Windows network, you'd use something like //host/share in this column.
The second column is simply the mountpoint, or the directory you'd like the filesystem attached to.
The third column is the filesystem type. It can be the type of filesystem on the hard drive, like vfat, ext3 or reiserfs or it can be a network protocol like cifs or nfs. Enter auto here if you aren't sure of the type or if the type isn't always the same (such as for a USB stick)
The fourth column is for mount options. Typically you'd just use default here. In this FAQ we used this column to set the umask for the filesystem, allowing users to write to it.
The fifth column is used by the dump backup program. This isn't used much anymore, so just put a 0 here unless you know otherwise.
The sixth column is the order in which the filesystems will be checked on every boot. Put a 1 for your root partition and a 2 for all other partitions. If a partition doesn't need checked, put a 0 here.