Are these sentences correct?

[Harry12345]

1 How do you do?
2 What do you do?
3 How do you do it?

Thank you!

[Raymott]

1 How do you do?
2 What do you do?
3 How do you do it?

Thank you!

Yes, they are all correct sentences.
The important thing is: Do you know what they mean?

[Harry12345]

Mr Raymat

Thank you very much!

Just now I asked a question: Is this sentence How does a small child do? correct? You told me it's wrong. So I asked this question: Are these sentences correct? You told me all of three are correct.

How do you do is correct? Why is How does a small child do? wrong?

And Mr Raymat, Are my explaination correct？

How do you do? means How are you?

What do you do? means What are you? or What's your job?

How do you do it? mean what ways will you use to do something?

[Raymott]

Mr Raymat

Thank you very much!

Just now I asked a question: Is this sentence How does a small child do? correct? You told me it's wrong. So I asked this question: Are these sentences correct? You told me all of three are correct.

How do you do is correct? Why is How does a small child do? wrong?
Because "How do you do" is an idiom used only in one very specific and fixed application. You cannot play with any part of it.

And Mr Raymat, Are my explaination correct？

How do you do? means How are you?
Yes.
What do you do? means What are you? or What's your job?
Yes
How do you do it? mean what ways will you use to do something?
Yes

R.

[Harry12345]

Mr Raymat

Thank you very much!

This is my first time to be here. I am very interested in English.I think I am very lucky to meet you here. I hope you can be my teacher.

Your student Harry

[Raymott]

Mr Raymat

Thank you very much!

This is my first time to be here. I am very interested in English.I think I am very lucky to meet you here. I hope you can be my teacher.

Your student Harry

Thanks.
You will find that most teachers here are helpful.