Isn’t it obvious what you can learn inside a classroom or the things that can be read from books and other learning materials? You get the foundation of what you really mean to learn but if you want to practice it, you will have to do more than just to stay inside the classroom and read books.
Learning a subject can only be complete if there is a practical sense in to it. This means that if you are learning a foreign language such as the German language, you will need to go out there and bring to life the words and phrases that you have learned. Speaking a language is the best way how to discover your flaws and if you ever have one (which is usually the case), you will easily adapt to its correct form. Not that speaking the German language has no room for anyone to have flaws and errors; nobody will ever learn this way.
They say the way to perfection is done through constant mistakes and it will no longer be the case if you become too afraid or shy of practicing your German speaking knowledge just because you don’t want to discover or know your mistakes. Make as many mistakes as you can and learn from each of them. When you do practice your German...