If you are interested in being a certified tax returns preparer, you will need to study for and take an official tax preparer exam, which will verify that you are fully capable of preparing people's returns. This is a test like any other, so any person with hopes of doing a great job on it and achieving a proper score will want to do everything they can to be fully prepared to answer the many various questions it will include.
When the day comes for you to actually sit down and take your test, you will be required to answer more than one hundred individual questions that will be presented as both true/false and multiple-choice. The number of questions may not seem like too big of a deal to everyone, but the fact that they are random questions that will cover any of thousands of different topics means that there is absolutely no way of knowing exactly what will be asked.
The only way you can possibly hope to be prepared for all possibly questions on your test is to learn every single thing there is to know, and there are plenty of great courses that are readily available to teach them to you, both local and online. You don't want to waste your time fooling with a guide that guarantees you a quick way to prepare, since there is no quick way, so do a bit of research and select the course that provides the best amount of information.
There is no one-size-fits-all guide for learning everything that is going to be on your test, because most of the people who will be taking the test have different levels of understanding of taxes and may require all available information. Since you will be seeing more than a hundred unique questions on the test that will be pulled from a list of thousands of possible questions, your best bet for getting fully prepared is to find a very comprehensive course that covers all the basics and gives you all the information you could possibly need.
Your goal is to get it right the first time, and since they will only be testing to ensure that you are competent and capable enough to understand the basics of preparing taxes, it shouldn't be overly difficult. As long as you take a thorough tax preparer exam course and take your time, answering every question you come to, you shouldn't encounter any major problems with passing and receiving your certification.