I recommend the ref guide first, may be just as "good night" book, to understand what is there in general.
But then visit groove3. Sonar, many known FXes, Synth, techniques and theory is there in a good format. $15 investment you will enjoy (if you have free time next 30 days...).
I am Russian, so I am rather paranoid when it comes to paying for software/tutorials/media content. My only excuse is that my own public software is free to use (and in case you will ever use any Controller with Sonar, you likely going to try it...). But Groove3 is a fair place.
Download ActivePresenter and try record yourself explaining any peace of software you use. Watch the result... That is what you normally see on YouTube (except professional advertisements). Groove3 has different level, for all videos they have at least 1-2 chapters you can preview. Compare with your own recording
Software producers have to sell you the product. And corresponding videos from them targeting exactly that aspect, if you stop after 5 seconds to open your walet, the mission is accomplished. Groove3 wants you watch next video, then next and so on. So they explain you useful staff, otherwise you stop watching and no longer pay...