today I got a message from one of my friend saying that "Hi Srini!, Yours truly turned 46 yesterday!!!" What does it mean?

"Yours truly" is a colloquial term meaning "I". Many English people sign off their letters with “Yours truly” - similar to “Yours faithfully”, “Yours sincerely” or “Yours aye”. It has come to mean “I” but is treated like a third person singular.

For example:

Yours truly has just passed his driving test.

This means:

I have just passed my driving test.