"Code" is the alarm. If the alarm is activated, it must be "deactivated" in order to start the vehicle. For my '96 328i, this is how to activate it. It's probably very different but as you said you dont have a manual so hopefully this will help a little. Turn the key to the '1' position (turn once,should only activate electronic equipment). You should hear a beep. Then, using the digit keys (my car has 4 keys, 1,10,100,1000), use those keys to create a digit code. Remember the code, because youll need it to start the car. Each time you turn off the car you must set the alarm (if you want it on). Otherwise the alarm isn't activated. The car wont start without the correct keycode.
Hope this helps.