How to learn Powerpoint through a tutorial online?

I’m familiar with word, excel and love publisher. At work they use powerpoint. It seems user friendly, but to really master and excel at it for work I would like to view an effective, easy (and one with no sound as I don’t have speakers) online tutorial during my slow times at work. Anyone know of a good one. I feel that there should actually be a powerpoint presentation of some sort that leads me through a good overview of the program.