“Can you tell me what my balance is?”

You're at your bank. You're talking to the bank teller and you want to know how much money is in your account.

Can you tell me what my balance is?

Can you tell me (embedded question)

This is a good way to ask for information from a bank teller, a store cashier, or a person you don't know.

You ask using an embedded question. So instead of asking, "What is my balance?" you ask:

Can you tell me what my balance is?

If you want to ask "Who is that?", you form the question this way:

Can you tell me who that is?

For more information on embedded questions, read here.

(someone's) balance

The "balance" of your account is the amount of money that you have in the account. So your account balance is a number. For example, the answer to the question above might be something like:

Your balance is $2,154.