I have been trying really hard lately to learn as much about Excel and its formulas as I can.  Sometimes it is difficult to find tutorials that are geared toward my skill level.  The best way that I have found to learn is to watch some free tutorials and follow them up by taking a Free Excel Quiz.  The quiz is kinda tough and really holds you to retaining what you learned.  It is really cool because it is interactive and gives you results at the end.  I will be working on watchign the videos and taking the quiz until I am comfortable enough with my new skillls.