What does 'speak' mean? The differences between the words 'speak, talk, say, tell'.

The meanings of the words 'speak, talk, say, tell' are similar. They are usually used to express something with words. However, there are small differences between them.

speak

It is used when referring to a person's speaking ability, speaking style and ability to speak a foreign language.

・Could you speak slowly?

・He can speak four languages fluently.

・He was speaking with an American accent.

・She lost her ability to speak after the accident.

talk

It is generally used to indicate the exchange of information or ideas between people.

・They aren't talking to each other.

・What are you talking about?

・You're talking nonsense.

・I don't like to talk politics.

・I don't want to talk about it.

speak or talk?

Both 'speak' and 'talk' can be used to express yourself to someone with words, but they are slightly different. The word 'speak' has a more formal use and indicates a conversation or speech made to achieve a result. 'Talk', on the other hand, refers to communicating or chatting in a more friendly manner.

・I want to speak to you.
 (On a specific subject, to reach a conclusion, to solve a problem, etc.)

・I want to talk to you.
 (To chat, to communicate, etc.)

say

It is used to give information with words.

・He didn't say his name.

・'I don't know,' he said.

・He didn't say a word.

・He said something in German.

・He stopped to say hello.

・He left without saying goodbye.

tell

It is used to report ideas or information to someone.

・He told us a love story.

・He is always telling lies.

・She didn’t tell me her name.

・Just tell me the truth.

・He didn’t tell me about the accident. 

・I can't tell you how I am happy.

say or tell?

'Say' mostly refers to saying something to someone with certain words, while 'tell' refers to telling something to inform someone about a subject. 
In other words, with say, there is no need to mention who the ideas or information were shared with, but with tell, there is. However, if a sentence with say identifies the person who was spoken to, to + the person must be used; but tell to is incorrect. 

・I want to say something to you.
 (Anything that can be described in a few words.)

・I want to tell you something.
 (About an event, a problem, etc. - usually for the purpose of providing information.)