When is aileron trim used?
Given your request to "answer with less smart words," it's hard to know what knowledge can be assumed, but I'll give it a try.

Let's say you're hand-flying the airplane straight and level, and you find that the right wing keeps wanting to drop, which you prevent by using left-aileron pressure on the control yoke. You can "trim out" the need for that left aileron pressure by rotating the aileron trim to the left (counter-clockwise).

Aileron trim is not often used for the simple reason that in normal aircraft operation, it's usually set where it should be from the previous flight.  In other words, you don't fuss with it unless you notice a need to fuss with it. In 12 years on 727s and 747s, I think I used aileron trim less than a dozen times.

The reasons that I can think of offhand that would make you want to fuss with it include:


The trim wheel was inadvertently moved (or deliberately as a bit of a prank) by someone.
A fuel imbalance has occurred between the fuel in the left and right wings.
You're doing a 3-engine ferry on the 747 or continuing a flight after having lost an engine.


To the best of my knowledge, all Boeing aircraft have aileron trim capability, not just some. Indeed, I would be surprised to find any transport category aircraft that does not have aileron trim capability.

Essentially, aileron trim can be used to to keep and airplane from responding to a situation where one side of an airplane is significantly heavier than the other side.