We can ask a direct question:
What time is it?
Or, if we want to be more formal or polite, we can ask an indirect question:
Do you know what time it is?
We make an indirect question by using a phrase and then a statement. Note that even though this is a question, we do not invert the subject andverb or use an auxiliary verb:
{indirect phrase} + {statement}
Can you remember where you put them?
Do you know how long the flight will be?
When the question can be answered with yes or no, we use if:
{indirect phrase} + {if} + {statement}
Would you ask him if the train has arrived yet?
Could you tell me if this is Athens station?
We can also use question words to make indirect statements:
{indirect phrase} + {question word} + {statement}
I don’t know what you saw in her!
She can’t decide where to go on holiday.
Useful Links
Questions in English Grammar