There are very good explanations in the manual. There is courseware, there is the Fusion section of this forum, there is the Fusion forum at www.steakunderwater.com.
Asking for a tutorial on 'the Fusion tag' in DR17 is like asking for a tutorial on a toolbox. It completely depends on what you want to achieve. Are you looking for motion graphics? Titles? High end visual effects? All of this can be done in 'the Fusion tag', so there is not one single tutorial for it.