Reusing my hard drive for a new pc question

[godro]

Hi, I want to reuse my hard drive from my prebuilt pc for a new pc I'm building. I've done a lot of looking but this topic specifically is confusing me a lot. My question is if I reuse my hard drive, can I simply plug it in or is it necessary to format it/use a USB as a boot drive first. And if the latter is the case how would I go about that process.

 

[USAFRet]

The physical hard drive? No problem.
The OS that lives on that hard drive? Almost certainly won't work. You'll have to do a full install of the OS.