How the sun came into the middle of solar systym?

Answer 1

It actually happened the other way around. The solar system formed around the sun. The Sun's gravity started pulling everything in that was within it's "reach" and these bodies became the planets. The sun comprises over 99% of the mass of the solar system. It's got almost all the matter so it's got almost all the gravity. Everything else responds to that massive gravimetric "anchor" and revolves around it.

Answer 2

The sun formed about 4.6 billion years ago from a giant, rotating cloud of gas and dust called the solar nebula. As gravity caused the nebula to collapse, the sun formed at the center, with the remaining material around it eventually forming the planets of our solar system. The sun's large mass and gravitational pull made it the dominant object in the solar system.