Updated June 12th, 2019.
Time was, you briefly pressed the power button on your Mac and you got this box:
In macOS 10.10 (Yosemite) (and in all macOS since), pressing the power button puts the Mac to sleep. If you’ve been reading this blog for long you know that Control-Eject brings up the old dialog box (the one you used to get by pressing the power button) but that’s not much help if your Mac doesn’t have an Eject key! See below.
Turns out that holding the Control key and pressing the power button gives the same result you used to get by pressing the power button alone, even if you do have an Eject key on your keyboard. Give it a try and see.