Hit ENTER after each Tag to add it to your post; Numbers in parentheses represent the Tag's usage.
Right-click on a folder, choose Delete Folder, and the message & preview panes don't update. You still see the messages in the folder that was deleted.
While we're on the topic, here's a suggestion. When creating a new folder, default the parent to Root when you're on the Inbox. Too many users build an extensive folder structure under the Inbox and that's not really the desired location.