How did the terrestrial and the giant planets planets form

They all formed in the same way, with everything from silt size particles to boulders slamming into each other and accreting into larger planetary bodies. Planets and dwarf planets start chemically differentiate even before the accretion processes stop, with iron, nickel and sulfur settling to form the core of the planet, followed by a predominantly Fe.Mg mantle that becomes more rich in silicon and aluminum further from center of the planet. Planets have crusts that are basaltic in composition, with surfaces where Fe/Mg minerals predominate over Si/Al minerals. Tectonic processes produce granitic "continents where Si/Al minerals with lower densities and specific gravities predominate.

Jupiter and the Jovian planets cannot be made entirely of gas. If they were, the solar wind would have dissipated them long ago. It is impossible for any planet NOT to have a liquid/solid core to provide the mass and gravity that hangs onto an atmosphere for millions to billions of years.

All of the Jovian planets (there's a reason I am NOT using the term "gas giants") have strong magnetic fields with higher dipole moments than the Earth's magnetic field. This means they all have inner solid iron/nickel/sulfur cores surrounded by a liquid outer core just like the Earth has. All of the Jovian planets rotate rapidly, which is required to maintain a magnetic field. Jupiter and Saturn MAY have layers of metallic and liquid hydrogen. It is physically and chemically impossible for the element with the lowest atomic weight and specific gravity (note that I did NOT say "density") to settle underneath iron and nickel to form the core of ANY planet. Liquid and metallic hydrogen also cannot maintain an electric current strong enough to create a magnetic field because of electron degeneracy. That means that when the electrons become dissociated from the protons and neutrons of their nuclei they just wander around aimlessly. They do not create much of an electric current, therefore no or very low strength magnetism.