I came into Electrical Engineering a different way than most - starting as a graduate student with an undergraduate degree in Microbiology. These two disciplines are slightly different - Microbiologists use microscopes and EE's use oscilloscopes :) I knew I had some catching up to do and remember one of my major goals for the summer before I started grad school was to learn how to use an oscilloscope. Fortunately I came across a free tutorial booklet from Tektronix on understanding and using an oscilloscope which made it pretty easy.
Well, even though that was over 30 years ago now, the Tektronix free tutorial materials still exist and they are even better than before. If you are starting from scratch or just want to brush up these are highly recommended. Here's a link to the tutorial page. Good stuff!