This book will teach you all of the main points of Old English grammar and a good chunk of the most common words in the language (around 1300, in fact). But it will teach you these things in a rather strange way: simply by telling a story.
The idea is that, by reading along to an engaging narrative that starts out simply and progresses only gradually in complexity, you will absorb the patterns of Old English and come to an implicit knowledge of the language. This knowledge will be implicit in the same way that your knowledge of your first language is.
Aiming at implicit knowledge makes for a different kind of textbook than you may be used to from any courses you’ve taken that have taught explicit knowledge of the language. You won’t find many verb and noun charts in this book. Instead, you’ll see all the verb and noun forms you need used throughout the story. By reading the story – granted, you will have to read it many times – these forms, although strange at first, will gradually become natural to you. They’ll become as natural, at least, as the many strange things your first language does (and all languages do strange things).
To get the most out of this book, I recommend the following approach: read each chapter a few times. First, read it casually, trying to get the gist of what is going on. Then, go through it more deliberately, trying to understand the meaning of every word (There are “word-hoards” after every chapter and at the back of the book which will help with this). Finally, read it through quickly once again, integrating your knowledge of the words you just learned on the previous reading.
Undoubtedly you will miss things. But the book isn’t going anywhere, and they’re not making any updates to the Old English language anymore either. Later on, you may come back to the chapter and notice something you didn’t before.
This also means that, if some aspect of the grammar isn’t clicking right away, don’t worry about it. It’ll probably make more sense later on.
On the topic of grammar: Old English is a language where words change to express different grammatical meanings. Sometimes they change a lot. You can easily find charts describing these changes online. I won’t dissuade you from looking these up; if you’re interested, they’re easily found. But they aren’t necessary to this method.
For now, just relax and get ready to hear the story of a very special bear.