Using a Paper Corner
Connect the two points with a line segment.
Use the corner of a piece of paper and line it up with the line segment, then make a mark from the corner to the other point.
Now rotate the paper, so that the corner moves to the other point. Since we know that the corner is a 90 degree angle, we know we are forming a 90 degree angle. Draw a line from the point to the mark you made on the paper.
If you move the paper, you can see that we've just made the next side of the square!
Rotate the paper and move to the point that we just made.
We've just found the last vertex of the square!
Then finish up the square.
Using the Pattern on the Grid
Start by connecting the points and looking at how to get from one point to the other.
To get from point M to point N, we have to move up 5 and then over 3.
Use that pattern to find the next point!
Repeat it again, and you'll have the whole square!
But you should still check the angles with a paper corner to make sure that each one is 90 degrees!