If you are searching by yourself, for example via Google or in the Library catalogue, you will also find other sorts of sources than what your teachers consider to be scholarly literature. This doesn’t have to mean that they can’t be useful for your essay work in any case!
It could for example be about:
Student essays: These can give a certain overview of your subject and contain references to useful literature. They normally don’t carry any greater weight. It varies from subject to subject whether student essays are considered to be acceptable as sources: Check with your teacher!
Course books: These often give a broad introduction to the subject. They are generally reliable, but not always as in-depth or up to date as could be required for an essay. If what is said in the course books is based on other research: Try to get hold of that research so that you can show that you have read the primary source.
Reports/investigations from authorities: These give a societal perspective on the subject. They are in the first instance a type of political document, even though they are sometimes similar to research reports.
Reports and statistics from other organisations/companies: These can quite often be relevant. What is especially important, however, is that you can show that you have found out the purpose of the organisation and considered whether the contents could be biased.
General websites: Since anyone at all can upload material on the web the quality can of course vary. How you evaluate what you have found on a website depends primarily on who is behind it.