You use fsck to check for errors e.g.
#fsck -t ext3 /dev/sdX
The command above would check for errors on /dev/sdX and would consider the filesystem to be ext3 because of the -t option. Before using fsck, you need to unmount all partitions that you are going to check for errors. I would suggest that you switch to single user mode before running fsck, or run fsck from a live cd such as gparted