I might have the opportunity to teach AutoCAD at a local community college this coming fall so I have been focusing on the basics.
Polar Tracking is a great way to define a specific angle while drafting.
This is probably the most common way to define an angle. It can be a fast solution when selecting from the default angles but requires prior setup for custom angles.
Polar tracking is located in the “Drafting Settings” buttons in the lower left of the screen.
To change how the icons are displayed (as shown above) click this post: https://autocadtips.wordpress.com/2010/11/03/drafting-settings-buttons-in-the-status-bar/
AutoCAD Tips 
For “Polar Angle Measurement”, I check the “Relative to Last Segment” radio button because when you start the LINE command, for example, and start drawing or snap to another object, the Polar action uses the entity you just drew/snapped to as a base to work from. This works great when laying out watermains and you have to take bend fittings into consideration.