Where can I check the system log files?

[Nay Oo <nayoo.deb@gmail.com>]

Hi

Today, I installed "telnetd" program in Sarge and system freezed totally 
at gdm login screen after reboot.
After that, I booted the system in recovery mode and uninstalled 
"telnetd" program. Only after that, it worked normally.

I want to check the log files? May I know where/which are the log files 
I need to check to investigate problems? Where are the locations of the 
log files in Debian where users can check when something strange things 
happen like that.

Any helps or suggestions will be very much appreciated.

Thank you,
Nay Oo