I'm not sure how many it wants you to move across the Y-Axis, so I can't help you with an exact answer, but I CAN help you by telling you how you do it
On every graph like this, you have an X-Axis, and a Y-axis. The Y-Axis runs vertical (up and down), and the x axis runs horizontally (think horizon, as in long stretch, Horizontally means from left to right, like a horizon)
When the question says, "Across the Y-axis" it is asking you to move what's on the graph (in this case, shape MNPQ) across the Y axis, meaning the vertical line. Basically, since this shape is on the RIGHT of the Y-Line, then you need to move it a set distance to the LEFT of the Y-line (aka: Y-Axis)
Now, in other words, you will be moving the shape to the left, and to no other direction, just a straight line to the left. Now, what the question DOESN'T say in your pic is how FAR to move it.
Let's do an example though, and say you want to move it 4 units to the left. You would pick ONE point, (use Point M) and move it 4 squares to the left. Then, put a dot where you land. Then take the next 3 points, and do the same for them. Then draw a line between the points, and you would have successfully moved your shape.