The Basics of X-Axis Reflection
Imagine a single point. Note the x-axis has been enlarged.
Then you take that point and jump it over the x-axis. This point was 2 units above the axis so it ends 2 units below the axis.
Now picture doing that same movement to every single point on the graph. The entire graph becomes a mirror image of its original self.
The V-shape originally faced up, after being reflected it now faces down.