Speak and talk have similar meanings. They suggest that a person is using his or her voice, or that two or more people are having a discussion. We can say: speak to somebody talk to somebody speak to somebody about something talk to somebody about something But we say: speak a language NOT talk a language talk nonsense NOT speak nonsense. Speak to and talk to are used more often than speak with and talk with. When you use talk you are refering to a conversation, it means that there are 2 or more people implicated in the action but if you use speak it is possible that sb is giving a speech or putting sth across, presenting a project or sth similar to it. For example if you attend classes and the teacher explains something (sth) to you he is speaking about your doubt, but he is the only one speaking in the class and you are taking benefit of the explanation so it is like if he is putting sth across. I hope it will help to clarify a bit your doubt.