Right-Click on the "My Computer" icon either on your desktop or in the Start Menu and select "Manage."
A new window titled "Computer Management" comes up. Select "Storage" from the left hand side by clicking it once, then select "Disk Management(local)" from the right side by double-clicking it.
Now in the lower part of the main frame (right side) of the window you should see a nice visual of all your hard drives. Each line is a different drive. Each box on a line (with a colored bar at the top and a size displayed in MB or GB) is a partition on the drive. Partitions are separations of space on a drive. Unless you are doing something specific that requires multiple partitions, you only want one partition per drive.
First you must delete any existing partitions on the drive you are going to format. Do this by right-clicking on the partition's box and selecting "Delete Partition..." Since you already know that you will be deleting everything on the drive, and have already backed everything up, you can safely say yes to any warning the computer presents you with.