Nightstand mode is enabled when the Watch is on its side and charging.
It's a sort of a skin that makes it look like a bedside clock, shows the time in big sized numbers, shows when the alarm is going to ring, lits up slowly and brighter as the time of your alarm time approaches, and the physical buttons (pointing upwards) will act as the snooze and the stop buttons.
The display doesn't stay always on but it will turn on every time it senses movement with its accelerometers (for example, a slight tap on the bedside table would be enough) or it's touched itself.
It's pretty nifty.
https://support.apple.com/en-us/HT205045
Wow that's actually really cool. I might look at one like that instead. I assume I could get a dual one with a lightening connection to plug my phone into using one plug?