One of the first things Sharepoint will ask you to configure when installing is where to put the ULS files (Unified Logging Service). This is were Sharepoint dumps all it’s log files and those Correlation IDs.
Used to be a problem to try and find the current log file and make sense of the entries when opening in Notepad.
The ULSViewer is a great tool to help analyze problems via the ULS log files. There is no installation, just a simple exe and allows you to open old log files or just the current ULS stream, which is great for troubleshooting. I usually open the ULS, then do something on my sites which cause errors and check back on the ULS to see what happened. It also provides the ability to filter on types of log entries e.g. info, warning, errors etc
You can find it here