Nokia offers user guides for its cellphones on its official website, Nokia.com. The documents include all kinds of safety, usability and connectivity instructions for each device.
In order to access the official manuals for a Nokia device, go to Nokia.com and click Let's Go. Then, click the Support button on the horizontal menu, and either select your device in the list or type in its model at the search bar. If you have trouble finding your phone's model name, click the link to the right of the search bar. After selecting your phone, scroll down and click the "PDF" icon inside a rectangle with title of the guide next to it.