Questions and "do"
You're (probably) an ELL, and depending on how long you've been speaking English, you might say sentences like…
"You drove here?" instead of "Did you drive here?"
"He wants to come?" instead of "Does he want to come?"
"Mario talked to his boss?" instead of "Did Mario talk to his boss?"
Sure, these questions are all grammatically correct, but they're a type of echo question and they might not be what was intended. An echo question is when you repeat part or all of something that was previously said or established, and then add a question mark. If you actually wanted to know if Mario talked to his boss, you'd ask a yes/no question.
So what's the difference?
In English, you don't move around anything in the sentence to make an echo question. That's why it's called an echo question. Echo questions in English are structurally the same as yes/no questions in Spanish, which is why ELLs have trouble with this.
To turn a sentence into a yes/no question in English, you either move the helping verb to the beginning of the sentence or you insert "do" at the beginning.
Here are some more examples of turning declarative statements into yes/no questions in English:
Claudia has never eaten a snow cone.
Has Claudia never eaten a snow cone?
She thinks they're too cold.
Does she think they're too cold?
She'll probably eat one at the Snow Cone Convention.
Will she eat one at the Snow Cone Convention?
Echo questions are usually used when you want clarification or you want to express disbelief. You'll find them in very specific conversational situations. Yes/no questions are more simple, straightforward, and common. Instead of clarification, you want a yes/no answer.
Here are a couple scenarios where an echo question would be appropriate:
1. You're in class with your friend Melinda, and she whispers that she went to the One Direction concert last night. You're surprised because you thought she was grounded. So you repeat, "You went to the One Direction concert last night?!"
2. You're at In-N-Out with your friend Carlos, and you notice that he orders his Double-Double with extra cheese. This is weird, because you remember Carlos saying one time that he didn't like American cheese. So you ask him, "You like American cheese?"
Here are situations (1) and (2), but altered so that a yes/no question would be appropriate:
1'. You're in class with your friend Melinda, and you notice she's tired. You don't know what she did last night, but you do know that there was a One Direction concert that she had been thinking about going to, so you ask, "Did you go to the One Direction concert last night?"
2'. You're at In-N-Out with your friend Carlos, and you both get Double-Doubles. As you're eating, you begin to think about how gross American cheese is when it's not in a burger. You're wondering if Carlos feels the same way, so you ask him, "Do you like American cheese?"
ELLs tend to have trouble with yes/no questions that have "do" because it has no semantic meaning (as a helping verb) and it doesn't exist in Spanish. If you need extra help, make some of your own flashcards.