Well, you need to partition your hard drive. Partitioning your hard drive designates usable space on your hdd.
And you need to format your hard drive. Formatting installs a file system on to your hard drive, it allows the operating system to read, write and overall understand the data stored on the disk. Without it, an OS cannot keep track of file locations, nor can it typically identify already used sectors (space) on a hdd. However, neither of these two concepts are tests.