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 and verb 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