Every problem has a surface, made of the details of your organization, your people and your field, and a core. Essence asks you to strip away the surface until you can name the core in a word or a short phrase. An animal shelter struggling to rehome its dogs might find that its problem is really about making a match.
With the essence named, you look for other worlds where the same essence appears: dating apps, house hunting, sports scouting. Those worlds have been working on their version of your problem for years. You study how they handle it, then carry their best moves home and translate them into your situation.
Use it when you're too close to your own field to see past its habits, ideas have started to flag, or you suspect someone, somewhere, has already solved a problem a lot like yours.