What will happen to our sun?

Don't worry, the sun isn't massive enough to become a black hole. In about five billion years, the hydrogen inside the sun would run out and the sun would slowly increase in size, engulfing the inner planets, including the Earth. (Don't worry. By then, we would have moved to Kepler 452b or something like that.)  Next, its outer layers will shed off, forming a planetary nebula, leaving the inner core, which comprises of mostly carbon and oxygen. This is normal as 99% of the stars in the galaxy would become white dwarfs. R.I.P sun.