I've had a hard time wrapping my head around the % operator because it seemed to me to be more in line with division and I couldn't let go of that image. But the way that I'm imagining it now is thinking about it as a remainder when dividing items and the output is the remainder.
I think about it in fingers, how many times does the denominator go into the numerator and what's the remainder.
5%5===05%4===15%3===25%2===15%1===05%0===NaN
This can be used to figure out remainders and what to use in the tail end of something. For example the Repeating Strings problem.