Once we can count, we can lay the numbers out in a row. A number line is exactly that: the numbers written in order, side by side, evenly spaced — the same gap from 0 to 1 as from 1 to 2, and so on.

The order is always the same: smaller numbers sit on the left, and bigger numbers sit on the right. So as you walk along the line to the right, the numbers get bigger one step at a time:

To find a number, you start at 0 and step right until you reach it. Press play, then replay it: a marker lands on a few different spots, and each time we read aloud the number it is sitting on. Notice that every jump to the right lands on a bigger number.

Khan Academy shows how to use a number line here: