Starting practically from scratch, each chapter increases a little in difficulty and adds more vocabulary and grammatical content. In general, the syntax is quite easy, since the idea is to be able to read rather than analyze and translate.
It tells, more or less continuously and with ascending difficulty, about present-day (1900s-present, that is) England and mostly about Julius Caesar’s incursion against the Britons.
Your task: read the text, then check the videos with my comments to make sure you have understood.