How do you learn online and is it effective?

Most of youtube is educational. There's wikis, blogs, articles etc. If you learn online with any of these, I want to hear about it. How effective is it? Do you retain what you learnt or does it feel like the time is wasted anyway? How do you improve your own learning? How do you take notes or improve productivity? I'm building Queso in this space and would love to hear from you.