Participation will count for a substantial part of your grade. More importantly, participating in class discussions is necessary for you to come to understand and develop your own views about the issues we'll be examining. This is true even for professional philosophers. We conduct philosophy primarily through conversation and argument with each other, not by sitting quietly at home.
Sometimes you may feel that you have nothing interesting to say, or you may not feel confident enough to advance and defend your own opinions. But remember that you can contribute to the discussion in other ways, too. If you feel uncertain about some issue, then you can help the group by asking questions to zero in on what the difficulty is. You can ask your classmates to clarify the meaning of things that they've said. You can ask them what their reasons for their claims are. And so on. These are all useful things to do, and they are just as important to the discussion as advancing your own views and offering arguments for them.
If you agree with what others have said, support them instead of remaining silent. Perhaps you can suggest additional reasons to believe their claims. At the very least, let it be known that you find their claim, and the reasons they offer for it, persuasive.
If you are shy or quiet, try to contribute to the discussion as best as you can. Ask questions, if you're not ready to advance and defend your own opinions. You should force yourself to contribute, however modestly, at least two or three times every section. Preferably, you'll be contributing a lot more than that.
Don't worry about comparing yourself to other students who are more vocal than you. Some people ask great questions in class but have trouble focusing when they write papers; other people are quiet in class but write phenomenal papers. So it is certainly possible to do well even if you're a little shy in section. Still, I do encourage you to speak up in section, to talk with the other students, and to ask lots of questions. This will really help you get better at philosophy much more quickly.
Treating each other with respect also means that you should give your classmates the benfit of the doubt, and interpret what they say charitably. If what they've said sounds utterly stupid to you, try to determine why they believe it. Is there some worthwhile point they're trying but failing to make? If so, help them figure out what it is.
You should listen to each other's opinions with respect, but you should also subject them to scrutiny and criticism. We expect you to defend your claims with arguments, so you are perfectly entitled to require others to defend their claims, too.
Remember that when others disagree with an opinion you've expressed, or when they criticize your reasons for holding that opinion, they're not attacking or insulting you. All of us hold false beliefs. The whole point of philosophical discussion is to try to find out which beliefs these are. We can't do that unless we subject our beliefs to this kind of criticism.