The question is not clear. What exactly do you want? what game are you talking about? Only game moderators can create new categories. You can either go to the forums of the specific game you are talking about, or contact the current game moderators about this.

If there are no moderators for the game, or they are inactive, there is a dedicated thread in the site forum for requesting to be game moderator.

Clearly. Go to the forum for the game you want a category for and ask there. If the game does not exist, request it.