How did the components of the earth come together to form the planet?

The Earth and other planets were formed in a protoplanetary disc of material orbiting the sun. Small solid grains of material collided and merged to form protoplanetary bodies. Theses in turn collided and merged to form increasingly larger bodies. Ultimately there is a single body in each orbit which is a planet.

The collision processes which formed the Earth would have generated a lot of heat. The early Earth would have been in a molten state. Heavier elements such as iron and nickel would have sunk to form the core. Lighter elements and compounds would be nearer the surface.

The solar nebula, a rotating cloud of gas and dust, is where the Earth's constituent elements—rocks, metals, and gases—were first drawn together by gravity during the solar system's formation. These particles then collided and accreted to form planetesimals, which then collided and merged to form protoplanets. Eventually, these protoplanets grew large enough to become differentiated, with heavier materials sinking to the core and lighter materials forming the crust and mantle. This process, known as accretion and differentiation, produced the Earth's composition as we know it today.