If I want to participate in a group conversation, how do I know when I can talk, and what to say so I don't make a fool of myself?

we are all here to help, listen and observe each others problems. you won't be judged here.your in a safe place

Stop worrying. Conversations are a free thing, full of life and movement and sillyness and comfortableness. If you want to participate in a group conversation (on 7Cups), just log on, say 'hey' or 'what's up' and then just join in. Whenever you have something to say, just say it. Everybody else is just as weird and foolish as you are and we all say something weird or at the wrong time. People just go with it. It's not that big of a deal. :)

You can only be a fool if you feel like a fool. If you want to talk. You should talk at a time you think is fine to talk.

You can talk whenever there is a pause in the conversation or it feels like a good time! And say whatever you want! You could try responding to what others said and relating to their topic.

Don't worry so much about it. Say what comes naturally to you. It might be helpful to remark upon what is being currently said and elaborate on it to help create a nice flow of conversation. But it's probably more important to know who you're talking to and knowing what they're comfortable with, so as to be aware of what not to say as well.

Social skills are all about having the good flow. Flow is not a random word: a group conversation is a big stream made by little personal streams merging all together. To ease the process you can visualize group communication as a river with waterfalls, other little rivers, muddy zones where communication stagnates and so on. You know your goal is to let the river flow and add some value (your value) to the group conversation. Speak when you feel the river needs more water, add your personal remarks, be welcoming towards "new rivers" merging. Try to keep up with the pace of the conversation, adjusting your rhythm accordingly.