First, a note about philosophy. I think of philosophy as first-and-foremost an activity, i.e., the activity of raising and seeking answers to very difficult questions about concepts and issues that matter a great deal to human beings -- concepts like justice, goodness, beauty, truth, authenticity, and so forth. While a typical philosophy course will involve a lot of information (about important historical figures, empirical research, etc.), it's a mistake to think of the discipline of philosophy as a body of information for students to try to absorb, retain, and regurgitate on exams or in essays.
Since philosophy is primarily an activity, the learning process must involve some amount of participation. Taking a philosophy course without contributing to class discussion is a bit like taking a cooking class and refusing to handle food. If you're not there to cook, you're not really there to learn. Likewise, if you're not in class prepared to ask questions, raise counter-arguments, etc., then you're not really there to learn.
Now, I understand that many students, for various reasons, are uncomfortable participating in discussion. Maybe you're especially anxious in social settings. Maybe you have personal issues with other students in the room. Maybe you have moral, political, and/or religious beliefs that you feel some pressure not to reveal in certain contexts, like a college classroom, for fear of social repercussions. I don't want to belittle any of this; but none of it changes the fact that learning philosophy requires participation. Nor will it change the fact that participation will be a significant part of your overall grade in the course.
All I can do is promise you that it's worth it. Philosophy students (even those who are not majors) regularly report feeling as if they become better thinkers as a result of taking philosophy courses, while also, in some cases, using these courses as a unique and rewarding opportunity to call safely into question some of the beliefs and values they've been taking for granted for most of their lives. But, not coincidentally, these reports tend to come from students who regularly added their voice to the conversation.