The explanation I've given a couple of times for people who are completely non-technical and just want a basic intuition for how cars turn gasoline into forward motion goes something like this:

-Gasoline vapor is highly flammable, and when you fill a confined space with flammable vapor and ignite the air, it causes a small explosion.

-If you set things up carefully, you can use this kind of explosion to push really hard on something, just like firing a cannonball out of a cannon.

-The way a car engine makes the wheels spin is very similar to pedaling a bicycle. When you push down on one pedal, in addition to driving the wheel forward partway, it also maneuvers the other pedal into place, ready to be pushed down next. When you get down to it, powering a bike is just a sequence of well-timed downward pushes in an alternating pattern. The bike takes care of the rest.

-A car engine combines the two concepts. Instead of human feet, it uses small, controlled gasoline vapor explosions in a repeating pattern that "pedals" the car's wheels and causes the car to move forward.

-The timing is crucial. All the complicated engine mechanisms you see are there to "reset" each explosion chamber (like reloading a cannon) so that it's ready to go in time for the next push: flushing out the exhaust gases and refilling the chamber with fresh aerosolized gasoline.

So there you go. Cars are basically just 4-wheeled cannon bicycles.