To make a long story short, and readable; The old computer I had ended up had the motherboard crash, so I decided to build a completely new system, because it would be fun and a great experience.
I have the DVD-RW optical drive from the old computer that I'd like to use as my main optical drive on the new build, and I'd also like to use the hard drive as the main drive of this new build as well.
It's a 1.0TB SATA/32MB Cache Western Digital Hard Disk Drive, but it's not formatted and still has all of the data from my last computer.
This is my first build and I don't want to buy a new HDD if I have something completely usable. I'd like to mention that I have some knowledge about computers, but I feel like I don't know enough to make a decision like this, and I'm not sure how to exactly think of this drive; usable or not usable.
Should I format this HDD before using it as a main drive? or can I just use this along with my new system? I'm just confused about this area and I hope someone can make this much clearer for me to understand.
It is fine to use it. If you are going to use it for the OS you can install on it without formatting. If it was the OS drive for your old computer you will have to do repair install at minimum to work with the new hardware.