Evaluate moveable points on a graph

I am new to working in the computation layer and I can’t seem to find how to make this work… I created a graph with four moveable points (A, B, C, and D). Each point has to be moved to a specific coordinate on the graph to create a rectangle. What coding do I write in CL to evaluate the location where the points are placed. I am not looking for students to get feedback. I just want it to show correct

Well unless you show us the code, “I created a graph” doesnt tell us anything.