Mendeley is a fairly straight forward reference manager. This section will cover Mendeley basics as well as the different ways you can do things. Take a look at them all and see what works best for you:
Creating your Library
Selecting citation styles
Using the PDF viewer
To navigate, use the links to the left or the drop-down menu at the top of the Getting Started tab. Each section will have video tutorials, simple step by step instructions and a few more details about the topic.