Pretty much everything that occurs on your machine is written to your event logs eg Services starting/stopping, Application Alerts/hangs , System crashes , Authentication/log on events ,
You cant really teach anyone how to read the event logs there is a art to it i have spend years looking at event logs on Servers/PC you need to know what your looking for. For example lets say you cant get a IP address from a DHCP server from your event logs i could diagnose the issue and find the issue for example the DHCP Client service had crashed/Stopped.
but to keep it simply
Application logs - Any events related to Applications you have installed on your machine eg Antivirus , MS office
System - System related events
Security - Authentication / auditing events