So, how do I find out why my system crashed/restarted?

[Shivetya]

In the last month or so I have had some issues with my 2013 iMac to where it simply freezes and either goes black to reboot or drops me back to the user and password screen. Where do I need to look to determine why this happens?

This mostly if not always happens when World of Warcraft is being played, it has happened with and without something streaming in a browser and happened with both native video drivers and Nvidia drivers (378 version as later versions are bad)

 

[treekram]

Open the "Console" app (use Spotlight or you can navigate to it in the Finder - from the Applications folder, it's in the Utilities folder). Click on "System Reports" and look for items that start with "Kernel_" and end with ".panic". You can post these. If you can look through them and see if they are similar, you just need to post one. If they are different, you can post maybe the last 3 or so.

Unless you have experience looking at these kernel panic reports, it may not make much sense. However, among the system reports available through the Console app, these are the typically the most useful for diagnosing problems using forums like macrumors. The other reports can be very long and may contain information that would seem to indicate that there's a problem when there really isn't a problem. These are mainly useful for the people at Apple.

If you don't find kernel panic reports, it might be more useful to give Apple tech support a call. Given the description of your problem, it sounds like a software bug somewhere. You may also find it useful to go to forums which deal with World of Warcraft or games in general on the Mac.