Help me figure out what to do

Okay, so I am soon going to, finally, build a proper gaming system. And I need a bit of help when it comes to figuring out how to move from my current hard drive to my new SSD+the old hard drive, while keeping everything other than the C: drive from the old hard drive.

Basically, right now I only have a hard drive, a 1 TB WD drive, with 3 partitions, that is the C: drive and two secondary partitions. What I want to do is, take this HDD out of the old system, and use it in the new system, but I don't want the OS to be on the HDD anymore, but rather on the new SSD that will be present in the new system. So, I am guessing I will have to wipe the C: drive from the hard drive(using the older system), install Windows and other apps on the new SSD(on the new system), and then install the old HDD into the new system, right? Hopefully this is not too confusing, though it certainly sounds so.