Effectiveness - How well the user achieves the goals they set out to achieve using the system (process). Efficiency - The resources consumed in order to achieve their goals.
In Software field, these terms are primarily used to indicate the effort put in to develop the Software and How much is customer satisfied with the product. Effectiveness signifies how well the customer requirements have been met i.e. does the final product provides the solution to the Customer problem effectively.
Efficiency is something, which is internal to the Organization that produced the Software product. It is basically- how efficiently the available resources (time, hardware, personnel, expertise etc.) were utilized to create the Software product.