2nd HDD
Yeah absolutely, assuming you have the physical slot for it.
I haven't done it in awhile so I can't remember, but you may have to go into bios to enable it.
Then you can go into "Disk management" to create a partition and it will create another drive. Though depending on your price range, you may want to get a ssd and switch your hdd to extra storage. Samsung ssds come with a magician tool for easy cloning, which lets you move your os over without much trouble, and prices are dropping pretty low for them. I did it awhile back with my laptop and it sped it up like crazy.
edit: should clarify. Switching which one is the primary is a little more involved, but is definitely doable. Better if you have a backup device or maybe just your phone so you can look up instructions/help if you get stuck along the way.