This iRacing how-to video covers how to use the built-in radio; add channels, talk to your friends, and communicate with other drivers. This video will also give you the basics so that you can spot for your friends and call out traffic. Also, you will learn how to ghost race against other drivers. Ghost racing is one of the best ways to practice without impacting any other drivers.
Although the computer generated iRacing Spotter can relay invaluable information about the cars around you, it still is limited in what it can do to inform and assist the driver. Having a spotter gives you more realtime feedback about the things happening immediately around your racecar, as well as allow a second person to assist with strategy.
for more information on spotting, see the link here.
One of the best ways to learn in iRacing is by utilizing 'Ghost Racing.' Ghost racing allows users to enter a populated race or practice session, but as a spectator that is invisible to any of the regular drivers of the session.
This is a great confidence-builder, and it's a great way to learn your way around a new track -- and even better, if you join a race session you can actually use this method to practice race starts.
For more information on ghost racing, see the link here.