The first column is the actual device name - for instance /dev/hda1 for the first partition on the first IDE hard drive.
The second entry is the mountpoint, a directory where the you mount it so you can access the files on the partition (unless it's a swap partition).
The third is the partition type - "ext2" for ext2fs, swap, proc, reiserfs and so on.
The fourth is for the options to use with the mount command. They are comma-separated and vary depending on what filesystem type it is.
The two last ones are fsck (filesystem check) options that indicate in what order the partitions should be checked on bootup or manual fsck, it at all.
For more info, try man fstab and man mount.