That's fair, I won't say that it's not as complicated as it sounds because I don't know what you know, but if you want it put into simple words, it's the following:

1. Install drive 1 in PC
2. Install Windows
3. Remove drive 1 from the PC and put drive 2 in its place
4. Install any Linux distro that comes with GRUB as bootloader (most of them, personally recommend Fedora if you want a suggestion)
5. Install drive 1 into the second slot that was left empty up to now
6. Start boot, your motherboard will have a specific key to launch the boot selector, e.g. F10, or go into the UEFI settings to put the Linux option first
7. Boot into Linux and trigger the GRUB detection for other OSes so it updates the list of entries
8. Reboot
9. Now without having to smash a random key to get the built-in boot selector, you will instead be able to choose comfortably from GRUB.

Anyways don't pressure yourself into doing any of that if you don't feel comfortable with it, of course.
One step at a time, the important thing is you're satisfied with what you have and that it's functional to your workflow