Do and does are auxiliary verbs, they are used for making negative and interrogative sentences in your speech. Do is correct with such pronounces as I, you,we they,for example,I don't know, we don't speak English, do you play football? Etc. Does is used with he,she,it: he doesn't like FB, it doesn't mean anything, does she drive a car?etc.

Hello Rahul! This is a great question and there have already been some great answers. Take a look at these example sentences. I don't have a car. You don't have a car. We don't have a car. They don't have a car. She doesn't have a car. He doesn't have a car. It doesn't matter. :) The difference is the subject and you can see it clearly by paying attention to the subject pronouns.

I don’t know You don’t know He doesn’t know She doesn’t know We don’t know They don’t know I can’t really explain the difference but this is how they are used

Don’t is for first person singular & plural and for third person plural.