speak、talk、say、tell 都有“说”的意思，但它们的意义和用法不同。

speak“讲话、发言、演说”,后面跟人做宾语要加介词 to, speak 作及物动词时后面跟各种语言；

Can you speak French? 你会说法语吗？

Who will speak at the meeting? 谁将在会上发言？

May I speak to John, please? 我能和约翰讲话吗？或 请找约翰接电话好吗？

常用的短语：

speak out 畅所欲言，直言不讳的说

speak up 大声说，毫不犹豫地说出

talk“谈话、闲谈”,是不及物动词, 后面跟人的时候用介词with、to 等, 后面跟“事情”要用到介词about ；

Who is talking to your mom? 谁再和你妈妈聊天？

Mr. Chen wants to talk to you. 陈老师要和谈谈。

What are they talking about? 它们在聊啥？

talk 常见的短语还有：

talk down ：以高声或连续的话说出

talk into 说服......做......

talk of 谈到，表示要

talk over 讨论（事情）

say 是及物动词，表示说的内容，即说了什么话；

What did you say? 你刚才说啥来着？

He said he would come to join us. 他说他回来加入我们。

Say no to smoking. 拒绝吸烟。

What he said made me very sad. 他说的话叫我很伤心

tell 表示“讲述、告诉”是及物动词, 后面首先要跟人, 然后再跟从句或者介词短语等。

Tell me if you need any help. 需要帮忙说一声。

Have you ever told a story about ghosts？你讲过鬼故事吗？

To tell you the truth, I don't like ghost stories. 说实话，我们不喜欢鬼故事。

另外，tell the difference 意为区别，如：

I can't tell the difference between you two. 我分辨不出你们俩谁是谁。