Do you need a training class to apply for a public institution?
If you are sure enough, you don't need to apply. If you have enough time and feel that you can't understand the book, you can sign up for a training class. You can also learn with the APP on your mobile phone. There are many such learning softwares now, some of which are also charged, but they are much cheaper than training courses. It shouldn't be a problem to do more simulation questions and papers.