How to revise or brush up the new android skill that iam learning here?

I take notes during videos, but honestly I find that I very rarely go back and review them. You can take notes on organizational-level things (like how the folder hierarchy is laid out, and what the different layout types do), these are what I tend to look back at the most.

But for the actual coding and how parts fit together, the best way to really internalize this is to PRACTICE! Download Android Studio and follow along, tweak small things here and there and see what works and how changes affect the app. Then try to build your own small app using what you've learned. Don't be afraid of making mistakes, I've learned so much just by fixing compiler errors! :)