do i have to read necessary the further readings? do the videos not explain it deeply?

That's a matter of choice really. Personally I tend not to bother with the additional readings unless it's something I'm especially interested in. You can always look them up at a later date when they become relevant to a project you're working on - it's much easier to take information in when you can immediately apply it to something you're working on.

The videos teach you everything you need to pass the quizzes/challenges, and to prepare you for future videos, so you definitely don't need to read every further reading to progress. Just know that at some point working on a project you'll likely come across something that wasn't explicitly taught in a video and you'll have to start looking up articles/forums/documentation to come up with a solution.