To install the MS Word add in (Mendeley Cite), from your Mendeley Reference Manager, in the Tools Menu, choose the Install Mendeley Cite for Microsoft Word option:
When installed the Cite add in will appear as below on Microsoft Word's References menu:
Note: if you are accessing MS Word using a QMU MS365 license on your device, or are using a campus computer or remote desktop, you will need to contact Assist and ask to be included in the user group for the Mendeley add-on.
When you are submitting your paper to an instructor or an editor/publisher, it is best to give them a copy that is "flattened", or in other words has the links to your Mendeley library removed. The in text citation and bibliography then becomes simple text that you can hand edit. This support document on the Mendeley support website has instructions to flatten a Microsoft Word document for both PC and Mac users.