-3 on a number line would look like 3 right from 0.
Let's just say we have a number line. A number line is a line that represents numbers. I'll say the positive side is on the top/left and the negative side (-3) on the bottom/right. -3 is a negative number. There is the sign (-) before 3. That indicates it's a negative number. Since it's a negative and 3, we move 3 down or right.