This is a really interesting question, and it's a question about questions. Let's take a sentence as an example: "Callum ate a lot of chocolate".

In this sentence, "Callum" is the subject, and "a lot of chocolate" is the object. Now, if we want to make questions to find this information, we need to make different kinds of questions.

In our example "Callum ate a lot of chocolate", if we want to make a question where the answer is "Callum", the question would be "Who ate a lot of chocolate?" "Callum ate a lot of chocolate." This question is looking for the subject of the sentence, Callum.

However, if we want to make a question where the answer is "a lot of chocolate." The question would be "What did Callum eat?"

"What did Callum eat?"

"A lot of chocolate."

So Solange's question is about the difference between subject questions - for example: Who ate a lot of chocolate? And object questions: What did Callum eat?

In the object questions we require the auxiliary verb "did", but in the subject questions we don't need the auxiliary. This works in the present simple tense too, so for example:
"Good students visit the BBC Learning English website."

If we want to get information about the subject - "Who visits the BBC Learning English website?"

If we want to get information about the object "What do good students do?"

So remember, for subject questions, where you want to find out information about the subject of the sentence, you don't need the auxiliary.

For object questions, where you want to find out about the object of the sentence, and you're using the past or present simple tenses, then you need the auxiliary verbs "did " or "do".

See also:
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