What are various theories regarding the formation of Earth?

The dominant scientific model is that the Earth and all the planets (and the Sun) coalesced from a molecular cloud, also known as a nebula.

Supernovae are the only known natural events capable of producing elements heavier than Iron, and since heavy elements exist on Earth (and in the Sun), the debris field must have come from a supernova.

Clouds of gas and debris which exist in space have centers of gravity which cause the debris field to collapse toward a central point. This process is known as planetary accretion. As the gravity pulls material in and bits of mass collapse, angular momentum is conserved and primary rotation(s) begin. The solar system as well as the planets all rotate due to conservation of angular momentum around various gravitational centers.

Of course there are other "theories," or beliefs regarding the creation of the Earth, but these are not based on scientific evidence. Many people believe the Earth was created instantaneously, out of nothing, by a deity.