说 (shuō) is the general, all-purpose verb for 'to speak, to say, to talk' in Chinese. It can take a language (说中文), a phrase (说一句话), or be used alone. 说话 (shuō huà) is a separable verb meaning 'to talk/speak' as an activity (e.g., 他在说话 'He is talking'), while 讲 (jiǎng) is more formal and often means 'to explain, to tell a story, or to lecture'. 谈 (tán) is used for discussion or conversation (e.g., 谈事情 'discuss matters').