Can I unplug my external hard drive?

My MacBook 2012-Mid requires a external drive to even boot up. I now want to turn my MacBook into a Windows 10, for gaming of course. But I want to know when using windows, can I unplug my external hard drive, and will it still work? (I'm guessing no because you require that hard drive to even make the MacBook work.) P.S, I'm unplugging it to put my epic gaming mouse, so can anyone give me a answer? Thanks!

(If you also can, tell me if there is a way I can not use my external hard drive, and use my internal hard drive, because I can't find my internal hard drive on my boot up screen, thanks too!)