You mean the thread prefixes? Go to the admin overview and then to -> Forums -> Thread prefixes. There you can create prefixes and groups. (Under „Applicable forums“: select the forums in which the prefix should be selectable) As soon as you created one, you‘re able to create a thread in the selected forums and choose your prefix there. - If you have installed the Resource Manager addon, you can also create prefixes for resources. This works exactly the same way.