Are we dealing with a laptop or a desktop? Are you looking to add the HDD for storage or for installing the OS on it(with multiple partitions)? If on a desktop, you should power down your system, connect the SATA power and data cables from the PSU and the motherboard(respectively) to the HDD. If you're installing an OS onto the HDD, the installer will allow you to format, create partitions and finally install the OS onto desired partition.