Not really sure what you're asking - are you trying to add a new HDD to a Mac? (edit: nevermind, that's what you're asking)
Usually on first boot of a brand-new drive, OS X says "oh, hey, you added a new drive - what do you want to do?" and you have choices of initialize, eject, and ignore. If you eject, then if the drive is hot-swappable you can remove it. If you initialize it, it'll format it 1 partition with HFS+, with or without journaling, MS-DOS (FAT32), or the Unix file system (UFS). If you Ignore, you can then launch Disk Utility and partition it however you want. Regardless of how you initialize/partition, it'll auto-mount the partitions. If you want to unmount one or more partitions, drag them to the trash can (which turns into an eject symbol). Ejected disks can be re-mounted in Disk Utility by highlighting the disk/partition and clickign the Mount button.
The big thing is if you replace the boot drive on a Mac - in that case, you'll boot from your OS X disc, then once the installer is loaded, go to Utilities -> Disk Utility and then partition/format it.
I do not understand what I do. For what I want to do I do not do, but what I hate I do.