It's used primarily in British English when people meet at the very first time. It's a synonym expression for "Nice to meet you"

How do you do is really just a standard greeting. And formal too. Muslims would say, for example, “ salamah walaikhum, which is a similar neutral greeting. Hope that helps.

Did you take the idea..? If the answer is not I can give you more examples about the Tag questions.

How do you do Means how are you

How do you do, in question means Describe the manner how you do something. Example, you if you are making some beautiful hats to sell them and Mary ask to you, Wow nice job! How do you do that? And you answer her Well, I take three pieces of colored cloth. A piece of double cartoon...and so on. When you look how in the sentence It means you should to describe something. However, ...