Some of the best documentation on the most popular and common programming languages can be found on W3Schools. You can also test very simple code here too, which is nice if you are going back and forth between writing code or need something to copy and paste.
Site description:
“W3Schools offers a wide range of services and products for beginners and professionals, helping millions of people everyday to learn and master new skills.”
Tons of exercises and tutorials, ability to get certified, and there is a guided path you can take here too. Almost Duolingo-esque in its approach to learning. Labeled as ‘the world’s largest web developer site’. Also gives you guidance on where to begin.