The easiest way to explain this is to include a graph. Notice how the graph runs from lower left to upper right. If you pick any point on the red line you will find that the number on the x axis = the number on the y axis. For example, put your pencil where you think x = 2 for the x value. When you find that looking down you should find that y = 2 looking to your left.
You could do the same thing with x = -2. Find that point on the red line going down. Now you should be able to see y = - 2 if you look right.
