You can click on the small circle on the x-axis, and drag it to the left or the right. The program will draw a tangent and a normal to the curve at that x-value.
You can reset the graph as a cubic or a quadratic.

Clicking the A, B, C and D buttons changes the graph.
By moving the small circle from left to right you'll how the tangent, its gradient and gradient graph are related. Play around.