Direct questions are the “normal” questions that we can ask friends, family members, and people who we know well.
Indirect questions are a little more formal and politer. We use them when talking to a person we don’t know very well, or in professional situations, and their form is a little different.
Whether we use direct and indirect questions depends on the situation, who we are talking to and what we are talking about. We tend to use direct questions with people we know well, in more informal situations and / or when the topic is not ‘sensitive’. Indirect questions are often used when talking to someone we don’t know well, in formal / professional situations, and / or where the topic might be ‘sensitive
When you ask a direct question, like "What time is the meeting?" you're being quite informal, some might even say abrupt, or even rude. You can make it more polite by adding please, "What time is the meeting, please?", but to be even more polite we rephrase it into an indirect question; "Do you know what time the meeting is?", or "Could you tell me what time the meeting is?" and if you want to be really OTT "Could you tell me what time the meeting is, please?"
Indirect questions differ from other types of indirect speech in both their construction and some of their uses, and they can as a result be problematic in both areas.
Here are some of the most common phrases used for asking indirect questions.