If you have a shortcut to open ESF directly, add a -console to the end of it. If you don't, then make a shortcut that looks something like this: C:\SIERRA\Half-Life\hl.exe -game esf -console
Keep in mind that is only if you are using half-life and everything is installed into its default directory, if you have the retail version of counterstrike or installed different things into different folders then you will have to change it around...
Anyways after you get that shortcut all figured out, use the ~ to open the console(to the left of 1) in game.