To find the force from potential energy on a graph, if the potential energy function U(x) is known, then the force at any position can be obtained by:

If the potential energy function U(x) is known, then the force at any position can be obtained by taking the derivative of the potential. 

The work done against conservative force is stored in the form of potential energy.

The change in the potential energy of a body is equal to the negative of the work done by conservative force.

$F=-\frac{dU}{dx}$