Yes. What is not correct is your putting the article "a" before grammar.
no_____If the sentence is You do do that (meaning You are in the habit of doing that) the grammar is perfectly correct and the sentence 'does have correct grammar'.
The correct grammar for this sentence is: "When did you send it?"
That sentence is grammatically correct.
No.
The correct grammar is "Between you and me."
"Roger and I appreciate what you did" is correct grammar
The grammar in the question is correct.
Yes, that sentence is correct grammar.
Yes, 'you were correct' is perfect grammar. An example sentence: You were correct when you said that a tomato is a fruit.
"Few days to go June will be ended soon" is not correct grammar. The correct grammar is "June will end in a few days to come." or "A few days to go until June ends."
Yes, this sentence is correct grammar.
The correct grammar for this sentence is: When did your friend come?