Source SDK: Mastering the Source/Help Menu
The Help Menu is one of the easiest on the whole Control Bar. It contains two simple buttons, which may prove very useful to you in development.
Help Topics edit
This button acts as a link to the Hammer Tutorial Directory of the Valve Developer Community Wiki. You can follow that exact link here: https://developer.valvesoftware.com/wiki/Category:Hammer
About... edit
This button opens a small text box featuring the copyright properties of the Hammer Editor and Valve Corporation.