The console in Fallout 3 is used as a debugging tool if you encounter specific problems during the game. Using this function is enabled and use cheats. To call the command line type the ~ button ("E") keyboard, which is located in the upper left of your keyboard under the Esc key. After clicking you will see the console interface and symbol blinking cursor "|", which should enter commands.
If after pressing this button the console does not start, then it's disabled in your version of the game. To make it enable, you'll need to edit the configuration file. Exit Fallout 3 and go to "start" - "Computer" - "Local disk C:". Select the Users folder - your user Name. Then open the directory My Games – Fallout 3.
Among the list of displayed data, double click on file FALLOUT.ini. Open the editor Notepad, where you will see the line iConsoleTextYpos and iConsoleTextXpos. Set the approximate location of the console on the display when it is called after pressing the button ~. For example, if screen resolution of 1024x768, you can enter in the following parameters:

iConsoleTextYPos = 800
iConsoleTextXPos = 300
String iConsoleTextYpos responsible for the called position the console window relative to the Y axis, and iConsoleTextXPos - X-axis, respectively. You will find the resolution of your own screen, you can launch the game and going to the window, its settings on the home screen. Among the options, select graphics settings, and view the numeric value is in "Resolution" (Resolution).
After specifying the required data, save the changes (File - Save) and run the game. If your settings were entered correctly, after pressing ~ in game mode you will see the running console.