How do I get started?

Checkout the getting started page.

How long does the creation of a video take?

It depends on the length of the video and complexity of the topic. But generally 2-4 work days. You can also find a 14h livestream creating a LiveOverflow video from start to finish:
[14:52:27] Making-of a LiveOverflow CTF video write-up 2019 (35c3ctf)

What programs/tools do you use to create your videos?

The livestream above shows everything in detail, but there is also a shorter version from 2017 here.
TL;DR: I record with OBS, then I use Adobe Premiere for the first round of editing, followed by Adobe Photoshop to create the overlays in a second round of editing.

What graphics tablet do you use?

There is nothing special about the tablet I use. I just bough an affordable/cheaper WACOM Intuos model.

Can you recommend me any books?

I have not studied using any books, so I have nothing to recommend.