There are two ways to add tags: you can go to your hub and then on the right side, a bit down, you can see your tags. You can simply add tags when you are logged in. This is the easiest way. The second way is to go to the tags menu when you are editing the hub. But the easiest way is the first approach: you don't need to go to edit mode for the hub when you just want to add or remove some tags.