Commas in complex sentences

An example complex sentence:
The one area that many students could improve is their puncutation because they tend to put in too much.
No commas are needed, however many students would try to put in commas.

This page from Towson University in the USA does an excellent job of breaking a sentence down into its separate parts and showing the difference between simple and complex sentences and how they should be punctuated. The link is here.