To sticky or unsticky a thread, you need either the moderator or operator role.

Sticky threads remain at the top of the forum they are in, which is useful for things like reminders or important messages.

To sticky or unsticky a thread, browse to the thread. In the top right corner next to the thread's title, the edit button takes you to the edit page.

If the checkbox for stickying a thread does not appear, you may not be logged in or may not have moderator or operator priviledge. Also note that you can only sticky a thread by editing it. You cannot set it to sticky during creation.