Hello, this is supposed to be a website built like a textbook, hence the name. Its purpose is to aid with school or, more generally, with the acquisition of knowledge on different topics. Commonly, when you don't get some new concepts right away, you refer to your notes. These, however, can sometimes look quite horrendous (no offense).
Usually, what we do is open our browser and search for some website that explains and illustrates the concept. You click on the link, open the website, and voilà, you get bombarded with tons of ads and popups. Summed up: It's all things that distract you from actually learning, and the only way to get rid of them is to buy some sort of subscription.
This website aims to bring you an ad and tracking, as well as a cookie-free alternative to just quickly looking something up. It is still in development and will be for quite a while, so expect some things to change or get added. With that out of the way, enjoy your stay.
*(This seems to be way worse on German websites than on English ones.)