How do you bind in Left 4 Dead

First of all you need the console. You can get the console by going to the Steam and open the My Games tab. Then right-click at the Left 4 Dead shortcut and select properties. Then click Set launch options and type -console to there. Then when you next time start Left 4 Dead you should have the console open. And the answer for you question you have to type bind "key" "command". So replace the "key" to key you want command to happen and replace the "command" for the command you want to happen. Example like if you type bind "F12" "ToggleConsole", then everytime you press F12, the console comes up. Hope that helped : )