speak - 用于“讲一些话是为了表达或传达感觉、信息、或是看法”；
eg. We can speak both Chinese and English.
say - 侧重于“出自谁口”,含有“表明”；
eg. We say, it's time to go home now. / What they said made me speechless.
talk - 指稍长时间的谈话,通常会含带出部分谈话内容；
eg. Free Discussion: How to talk to women on the phone?
tell - 同时侧重指向性和交流内容
eg. I told you she doesn't like it.
>Tell - v. Communicate information, facts, or news to someone in spoken or written words: "I told her you were coming";
>Say - v. Utter words so as to convey information, an opinion, a feeling or intention, or an instruction.
>Speak - v.
1. Say something in order to convey information, an opinion, or a feeling.
2. Have a conversation: "I'll speak to him if he calls".
>Talk - v. Speak in order to give information or express ideas or feelings; converse or communicate by spoken words: "the two men talked".
体会英文的defination,会帮助理解和运用这几个单词的.希望帮得到你!