A closed topic in the Forum module will still be visible to users, but the users wil be disallowed from posting comments on the topic. You can close a topic by following these steps:
- Go to the Publish page at the top menu.
- Choose Forum at the left menu.
- Click Add category and choose a name.
- Click Add forum in the overview or in the category.
- Underneath Forum settings you will see different options. Click the button underneath locked to ON.
You can also close a topic when you create a new topic in the Front End.