Different sources can be used for different purposes. Wikipedia may be useful to give you background information to help you gain an understanding of your topic but it will NOT be acceptable as a reference to support your assignment.
A scholarly or peer reviewed source is work that has been written by researchers and academics, and has been through a rigorous selection and review process prior to publication..
If you need to verify if your source is peer reviewed you can use Ulrich's Periodicals Directory. Type in the journal title (eg. Medical Journal of Australia) – not the article title – and you will be able to see if the journal is peer-reviewed by the little referee jumper symbol next to the title.
You can limit your search to peer reviewed resources by filtering on the left hand side of your Library Search results page.