It's definitely easy to learn once explained, and every enthusiast knows - but as a cyclist living near a popular bike route, I see a lot of casual riders who appear to have no idea how to use their gears.
The most common thing I see are riders with the cranked up in a high gear on flat land, and you can see them almost standing or straining to turn the crank. I cringe to think about the pain they are inflicting on their knees.
IME once you spend a few minutes teaching someone about their gears, they're usually shocked at how much easier and more efficiently riding is, and enjoy cycling much more.