Logic is the science of how to evaluate arguments and reasoning. Critical thinking is a process of evaluation which uses logic to separate truth from falsehood, reasonable from unreasonable beliefs. If you want to better evaluate the various claims, ideas, and arguments you encounter, you need a better understanding of basic logic and the process of critical thinking. These aren't trivial pursuits; they are essential to making good decisions and forming sound beliefs about our world.
Logic is not a matter of opinion: when it comes to evaluating arguments, there are specific principles and criteria which should be used. If we use those principles and criteria, then we are using logic; if we arent using those principles and criteria, then we are not justified in claiming to use logic or be logical. This is important because sometimes people dont realize that what sounds reasonable isnt necessarily logical in the strict sense of the word.