Ok so the drive I plan on giving to my father is my OS drive. So when I do this I take out my OS drive and then keep my other plugged in. Then I slam in the USB and boot from it and do all of the installation from there on? If I somehow manage to screw it up can I always take it to microcenter just in case?
Not quite.
You have this drive removed and in a drawer somewhere.
When the new system is ready to be built...
Then you connect that drive and only that drive.
Boot from your USB install media, and start the OS install process.
When it asks 'where', this is when you select Custom.
You'll be presented with a list of all existing partitions on that drive
Select each, and DELETE.
Leaving one large blank space.
Let Windows install to that, creating what it needs.