Useful - How to Troubleshoot Your Mac With Activity Monitor

Not many casual users know about OS X’s Activity Monitor, and fewer still understand how it works and what it can really do. Here’s how to use Activity Monitor to manage your Mac’s memory, fix slow applications, and troubleshoot various other issues.

http://www.howtogeek.com/227240/how-to-monitor-your-macs-health-with-activity-monitor/

Rgds,
Ed