谈话指的是2个或者多个人之间的交流，比如他们在谈话等。 说话相当于名词，比如说这个人说话真粗鲁。可以指个人或者多个人。 希望我的解释能对你有所帮助。（Conversation refers to the two or more communication between individuals, such as they were talking, etc. Speak equivalent to nouns, for example the people speak really rude. Refers to a personal or more persons. Hope I explanation can help you.）

"talk" is used 2 or more people in the conversation. "speak" usually oneway, giving a speech. I would say "You speak very rude." makes more sense. Here is an example sentence. When the teacher speaks in class, students should not talk to one another.