To speak –
говорить, разговаривать (больше как физическое действие)
To speak a language: - Tom speaks
English.
To speak to/with somebody: - Mark never speaks to a stranger.
To say –
сказать (что?)
To say something: - Jack says
that he is from UK.
To say to somebody: - Joeys said to his teacher that he wouldn`t be
late anymore.
To tell
– сообщать, рассказывать (кому? – что?)
To tell somebody (about) something: - Tom is telling his friend a funny story.