Right now your model consists of ngons. In most cases it is better to have quads than ngons in your model (see this topic- it explains it nicely: http://blog.digitaltutors.com/ngons-triangles-bad/).
To create them, select two vertices on the corner of your model and press J to join them with edge. Repeat the process in other corners.
Now your model consist of quads. You may add edge loops to your model to sharpen the edges (it would be impossible to do it having ngons). Hover your cursor over model and press CTRL+R). See the manual here: http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Meshes/Editing/Subdividing/Loop_Subdivide
