When you demonstrate something, you show what it is or how it works. To demonstrate how your new juicer works, you should have lots of kale, carrots, and beets on hand — and some brave friends to try your concoction.
Demonstrate comes from the Latin word demonstrare, meaning “to point out by argument or deduction.” To demonstrate a point you must make a valid argument and give examples of why you think it's true. Demonstrate can also refer to a public protest. You can demonstrate with your comrades by marching through the streets with homemade protest signs.