about critical

How often have ever thought of the word critical? In some ways, it is very new to me. I was a kind passive student. Though I have a different idea to others, I can't express my minds clearly. Why? What makes me be afraid of telling the hidden mind? I am not familiar with this class mood yet, and I need more time to be accustomed to it. Moerover, I want to find the purpose of this subject. After completing it, how useful it works in my clasroom... I wonder and I hope to give a good result .