Yes it does. We usually use this saying when we aren't sure of the answer. Many times we follow up with a statement like : 'But I really don't know much about the subject' or 'But I don't know for sure'. We use it when we can't use statements like 'Yes, it is'. or 'No, it isn't'

Yes it does. It means you agree to what was said using all the information that you have acquired in your lifetime. It doesn't include any information that you don't know of.