How do you use the arrow keys to show coordinates? After entering in a function y=x² (using the [Y=] key), adjusting the [WINDOW] coordinates, and selecting [GRAPH], you will see a screen similar to that below

Now, just press the arrow keys (the four blue arrow keys on the right hand side of the calculator). A "cursor" will appear along with a readout of the x and y coordinates (on the bottom of the graph).

If you want to restrict the cursor to lie along the curve, then use the [TRACE] key, next to the [GRAPH] key below the screen.