To view tasks for a specific tag choose Tags from the left side menu and tap the particular tag.
You can also choose how the tasks are grouped and sorted in this view.
To edit a tag long-tap the tag and choose Edit from the popup menu.
Make the desired changes and tap the disk icon the save the changes.
Add new tag
To add a new tag choose Add Tag from the menu.
Delete a tag
To delete a tag long-tap the tag and choose Delete from the popup menu.