What you probably need is fdisk (or cfdisk more user-friendly version) to create and delete partitions.
To make a filesystem (can also called as formatting) in to the partition you can use the command
mkfs -t type /dev/hdXX
Where XX is a letter of the disk + correct partition and type is the filesystem type (like ext2, ext3 or reiserfs).
You can destroy all your data with any of the tools mentioned here if not properly used.