You tell your printer "[Pantone] Green 0921 C" or whatever the color is. This is a compatible list with the same ID numbers.
You pick a spot color the same way you would have done it a month ago. And you print the same way you would have done it a month ago, except possibly with an extra annotation on the spot color.
The main use of this plugin is to let you actually see your spot colors instead of black while you edit. The secondary use is to give you a rough idea of the available colors, but you wouldn't finalize picking a spot color based on how it looks on a screen anyway, you'd get an actual sample.
Okay, so I’m a printer. You specify a free tone which allows me to get the SEMPLETONE+ which allows me to get the PANTONE with a simple database lookup, and I just need to pay PANTONE for calibration essentially.
There's zero point in designing with Pantone if you're not going to use actual Pantone. Just use any palette (including this one) then.