Loops are repetitive conditions where one variable in the loop changes. Loops are handy, if you want to run the same code over and over again, each time with a different value.
Instead of writing:
doThing(cars[0]);
doThing(cars[1]);
doThing(cars[2]);
doThing(cars[3]);
doThing(cars[4]);You can write:
for (var i = 0; i < cars.length; i++) {
doThing(cars[i]);
}