If you list a reference in the reference list, you should actually cite that reference in your written work.
Why should I cite sources that are listed in my reference list?
Your reference list should only contain sources that you cite in your written work. If there are references that are not cited in your work, the reader would have no clue on why that reference would apply to your work.
How do I cite sources that are listed in my reference list?
In some reference styles, references can be cited by the reference number, while in other styles references should be cited by author and year of publication.
More details on different reference styles can be found in the Reference style article.
Automated Feedback can help you with applying reference usage in the correct way.