If you like your spiffy new mechanical keyboard but want to use it on a Mac, you need to map the Command key and Option key around because on a Mac, it goes Control, Alt or Option and then Command whereas on a Windows keyboard it is Control, Windows-Key and then Alt.
This is really confusing for muscle memory. The solution is to remap the Modifier keys, you go to System Preferences/keyboard/modifier keys and then select the
USB Keyboard and then for Option Key map to Command Key and vice versa. Done!