NVRAM (PRAM) Reset Process

Created on: April 24, 2013
Last updated: July 21, 2015

The Apple document linked below provides the official instructions for performing an NVRAM (or PRAM) reset, as well as some useful background information on what the reset actually does inside the computer. 

NVRAM (or PRAM) resets can be a useful first step in troubleshooting certain problems with a Mac, however in most cases a standard Restart from the Apple menu is all that's required to resolve many temporary issues. For display resolution problems, audio volume issues, and startup disk issues, the NVRAM reset does provide extra benefits over a standard Restart.

https://support.apple.com/en-us/HT204063