Load game with the command line: hl.exe -dev -toconsole.
Then, press ~ if the orange text on the screen does not
disappear. During gameplay, press ~ to display the text
prompt and type in sv_cheats 1.
Press ~ and enter one of the following console commands to
activate the corresponding cheat function.
God mode /god
No clipping mode /noclip
Opponents ignore character /notarget
All weapons and ammo impulse 101
Map select /map