Loading the Editor
In Quake 4, like in Doom 3, the LevelEditor is actually part of the game executable. Load the game, then press Alt+Enter to go to windowed mode (you may experience issues loading it in fullscreen). Drop the console (Ctrl+Alt+~) and type 'editor.' (The period, while grammatically correct, is not part of the command!) Poof! You now have the editor up and running. Take some time to customize your layout and you're ready to go.
Setting up Shortcuts: To load the editor from a shortcut, copy your game shortcut and modify it as follows to form your editor shortcut:
"...\Quake4.exe" +set r_fullscreen 0 +editor
Your r_fullscreen settings are saved each time you run the game or editor, so adjust your game shortcut with:
"...\Quake4.exe" +set r_fullscreen 1
Here are some other useful parameters you can add to your shortcut:
+com_allowconsole 1: Allow access to the console by pressing ~. A must for testing.
+set r_mode X: Set your render mode (from 3 to 8). 3 is 640x480, 8 is 1600x1200. Useful if you run the game at desktop resolution; setting the r_mode lower for the editor will keep your F2 instances at a nice manageable size.
+set r_brightness 1: By default, Quake loads with r_brightness set to 1.2. This can be annoying when working in the editor, so reverting it to 1 will restore your normal desktop appearance.
+set r_multisamples X: Adjust FSAA (anti-aliasing) settings. If you have AA enabled, the editor will break. Set this to 0 on your editor shortcut and back to your desired AA settings on your game shortcut.
+set r_clear X: Setting this to 0 on your editor shortcut will cause your rendered view to display the void as grey instead of black. Set to 1 for a purple void. Also supports RGB values for custom coloring.
The Next Step: Building a Basic Room