Question

Does the graph represents a function

Answer 1

In this situation, we would use something called the vertical line test. In other words, if we can draw a vertical line that passes more than one point on the graph, then the relation is not a function.

If we use the vertical line test in this situation, it is not possible to draw a vertical line that passes through more than one point. Therefore, this does represent a function.

Answer 2

You could use a simple pencil test to figure it out.
Place a pencil vertically on the paper, and move it left to right or vise-versa 
When moving it make sure the pencil doesn't hit two points at once if it does it is not a function, but this is not the case

This is a function