Step: 1
In the main menu go to options. then click on Keyboard / Mouse

Step: 2
Find and enable developer console

Step: 3
Go to your steam library, right click on L4D2 and click on properties

Step: 4
Set launch options to: -console

Step: 5
Launch L4D2

If everything was done right, when you launch Left for dead the console will appear
If you wanna launch console again after closing it you need to bind a key in console, to do that
type in: bind "yourkeyhere" toggleconsole
For example: bind "o" toggleconsole

If you wanna open console with F1 to F12 then type: bind "F()" toggleconsole
For example: bind "F11" toggleconsole

After you done setting up the console press your binded key to open it up

No opening up a map from the select screen won't work you need to
open the map from console, to do that select your desired map

Mine will be dead center streets, to do that you need to type in the chapter number
and map number in consoles language, like this: map c1m2_streets

c1 = chapter 1
m2 = map2
streets=the name of the map

There is a website for this i'll leave it here
https://commands.gg/l4d2/map

Once you've selected your map click Submit and the map will start loading

So you've loaded into the map and got your console ready.

Now to do all the random stuff you want to just type sv_cheats 1 to the console
but why do you have to type in a number?

1 = True
0 = False
So when you type in sv_cheats 0 you are saying that you dont want cheats rn
but 1 means that you want cheats. There are many commands using this True false thing

There are many many commands you can mess around with but it would be hard
to type it in to 1 guide, you can just visit forums, pages, wikis about cheat codes anyway
so i wont be typing them here, The thing you can try is: noclip, give (itemyouwant), kill,
kill (playername), bla bla bla

Thanks for reading, i hope you found this guide useful.
If you did i would appreciate a Like.

If there is anything i missed out on please tell it in the comments

Bye bye and happy hacking!