Reply to any post directed to you in a courteous manner, unless there is good reason not to. Don't confine your chat to one person only, as others may take offense or feel left out. If you have questions, ask away, but in a courteous manner. Most people will respond in like manner, and, if your question is too personal for them, they will politely say so. Asking questions is an excellent way to start conversations.
Most people like to welcome and help 'newbees'.
If someone arrives who is being offensive, ignore that person. Report any such incident immediately to the chat service so that appropriate action can be taken. It is acceptable to give your email address to others, and to ask others for theirs. Giving out one's email address is a matter of personal preference, and declining to do that should not be taken as an insult.