All the information, quotes and examples that you use in your assignments must be properly referenced, partly to help your reader find the material if they need to and partly to protect yourself from any accusation of plagiarism. So, whether you quote a person directly or merely mention their work, you must include an in-text reference (giving the name of the author and date of publication) and add full publication details in a reference list at the end of your assignment.
Many disciplines use this system of referencing, which is based on the Harvard system. The OU library gives you more information on the Harvard system of referencing.
Referencing practices do vary between academic disciplines and modules so it is a good idea to check your Assignment Handbook for information on what style of referencing is preferred. One guide is to look at how quotations are handled in your module materials.
Tip for referencing
It's a good idea to use a number of different sources in your writing.