You've come to the right place!
Click and drag to pan around the screen.
Scroll to zoom in or out. Press "R" to reset the zoom level.
Double-click on the grid on the left hand side to plot a point.
The coordinates and edges will appear in the output box below.
You can also edit the coordinates in the box and they will be drawn on the screen.
Press "G" to toggle grid snapping. Grid snapping is currently ON.