So you finally built your PC - - well it's not finished yet until you install a new, empty hard drive in it, then install Windows on it or whatever OS you plan to use.
You can use your laptop's hard drive if your PC case has any 2.5 inch drive bays, otherwise you need to buy a mounting kit.
However, you cannot use the existing Windows installation that's on the laptop drive.
You must reformat the existing OS partition, then install a fresh Windows from scratch.
It would make more sense to leave your laptop drive alone & go buy a new 3.5 inch one for your new build.