Question

Why don't planet hit each other ?

Answer 1

Firstly,

Orbits are there. Orbits are formed when an object gets a barycentre which has a gravity that forces that object to revolve around it in a definite orbit around it.

A force, such as gravity, pulls an object into a curved path as it attempts to fly off in a straight line.

As the object is pulled toward the massive body, it falls toward that body. However, if it has enough tangential velocity it will not fall into the body but will instead continue to follow the curved trajectory caused by that body indefinitely. The object is then said to be orbiting the body.

Answer 2

as their orbit and axis of rotation is different

This artist’s concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. NASA’s Spitzer Space Telescope found evidence that a high-speed collision of this sort occurred a few thousand years ago around a young star, called HD 172555, still in the early stages of planet formation. The star is about 100 light-years from Earth

They did! The current solar system is the stable aftermath of a fairly violent growth period, so what we see now is the result of a several-billion-years-long evolution.

Many of the objects in the universe didn’t begin their existence in the same form as they are seen now- large objects are usually built up from much smaller objects, instead of appearing rapidly at full size. This holds for both galaxies and planets. The planets in our solar system started out just as slight clumps of dust and gas inside a larger disk of more gas and dust. There’s no particular reason for a fixed number of these clumps to pop up, and we fully expect that there were lots of them.