Deadheading refers to the removal of dead flowers either to encourage more re-flowering/re-blooming. Many annuals and perennials will continue to bloom throughout the growing season if deadheaded.
To deadhead your spent flowers, either prune or pinch them off with your fingers.
The first rule for gardening success is planting the appropriate plant for the location. Shady areas require shade loving plants just as a sunny areas require sun loving plants.