Word has its own, basic referencing system available via the 'References' tab on the ribbon. This lets you add references to a document and then create a bibliography at the end of the text. References are stored in a master list, which can be used to add references to further documents.
Note: this system is not as powerful as EndNote, Mendeley or Zotero.
Note that the styles available in Word might not match those required for your assignments. Check them carefully and if they don't match you can convert the bibliography to editable text. See the guide below for instructions on doing this.
Although this video isn't for the latest version of Word, it gives a clear explanation of the basics, which haven't changed.
Microsoft also have their own video on the page linked below left.