I start with wikipedia or the intro to the documentation. Then I read deeper on whatever seems interesting until I think I know enough to be productive. Then

I start with wikipedia or the intro to the documentation. Then I read deeper on whatever seems interesting until I think I know enough to be productive. Then I start using it. If I get stuck, I find more specific information until I'm not stuck. Rinse and repeat. So in short, I read the smallest amount of info possible to start and then let my practical experience guide me after that.