Learn only what you need to learn, when you need to learn it. The online help is good for that.
Platinum is a top of the line, sophisticated product. Learning it is no different from walking into a studio back in the day and expecting to be a recording engineer. The good news is that the slowest going is always at the beginning. Take one thing at a time - learn how to record, then learn how to drag in drum loops from the browser.
Think of it this way: Suppose you bought a musical instrument. How long does it take you to get good at playing it? A long time...but you can start having fun once you get past the basics. If SONAR was a guitar, you'd be in the "my fingers hurt, and how do you tune this darn thing?!?" stage.