Hello, and welcome!
Yes, you could physically switch around your disks every time you want to switch the OS, but that's rather cumbersome. It's much easier to
- Boot into the Ubuntu installation
- Tell it to install onto the second disk
- and let it install the boot manager.
The boot manager (
GRUB) can go either into the MBR (Master Boot Record) or the boot record of the second disk. The first option will let you boot either OS without any changes, but you'll have to do some work if you don't want that anymore. The second option will require you to tell the BIOS which disk to boot off every time (for recent BIOS versions there's a hotkey for that, usually the escape key).