Typically the system.log and exception.log file will exist in the
/var/log/folder. These contain most of the information you will need. You can check to see if these are enabled and what the names of the exception and system log are by going to
System > Configuration > System > Developer > Log Settings.
Report files are generated in this folder after a user has encountered an error. Each file only includes the details for one error. These are used in order to hide the error details from the public. On the error page there will be a report number which is a reference to the corresponding file with the same name in the