「話す」 (hanasu) means "to speak" or "to talk." It's used for verbal communication. If you speak a language, you use を (o) for the language. If you talk to someone, you use と (to) or に (ni) for the person. For example, 「日本語を話します。」(Nihongo o hanashimasu.) means "I speak Japanese."

話すは言葉で伝えること。日本語を話します。