The session debugger allows you to debug certain aspects of the ServiceNow platform during the ServiceNow session. You are also able to turn on or off all session debugging. Session debugging will give you a lot of information, but it can sometimes be information overload, so it can be worth picking individual aspects you want to specifically debug. I often find the security debug to be the most useful.
Session debugging is found in system diagnostics and contains a number of modules. You can enable any of the session debugging areas by clicking the module you would like session debugging turned on for. You can also turn on all debugging by selecting Enable All. You cannot turn off individual debugging areas, though, ...
