How to use your reserved slot when a server is full

1.) Open (CS:S or TF2)
2.) Press "Esc" button
3.) Click on "Options" to your bottom left of the screen.
3.) Click on the "Keyboard" tab on top of the window that opens.
4.) Find the "Advance" button the bottom of that screen and click it.
5.) Click to check the option "Enable Developer Console (~)".
6.) Now you can open your "Console" up.