When the box is already filled, it means that a translator has already translated the string. If the box is not filled, click on it and suggest your translation (if you are not sure don't do it and let another translator translate it). If you believe a translation is incorrect or could be improved, you can fill the box with your own translation (if the old one is already validated by a member of the Valhelsia Team, it will be put in the list of suggestions and will have to be validated by a manager in case it gets enough votes).