One of the steps when install will ask where you want to install the OS. It'll list your drives and you can choose to format the drive at that point.
Exactly. If it is on a pen, you can even create partitions, delete them, and do what the hell you want. Unless you missed that part.
I actually installed W10 2-3 times on my HDD by accident before installing on my SSD. Took a bit of time, but I got it running. Try installing, if you fail, google it and try again.