A chisel is one of the most useful tools in the workshop, but it's important to know how to use it. For example, after routing out a mortise for a door hinge, use the flat side of the chisel for cutting or neatening the edges of your work. Or use the beveled side for cleaning up or leveling off a surface without taking off too much at a time.
For more on tools, consider:
Top 5 Tool Buying Tips
Choosing Essential Tools for Woodworking