Jupiter is the 5th planet from the sun, but it's not at all like earth. Jupiter is a gas giant, a large planet that is not primarily composed of rock. There are four gas giants in our solar system, often called Jovian planets. Jupiter is unique because it is the largest and most massive planet in our solar system. It is more massive than twice all of the other planets combined, and is theorized to be as large as a gas giant can get. Any more mass and it would begin to shrink under its own weight to the point that its radius would hardly increase at all, and might even decrease as it collapses on itself.
The center of Jupiter is believed to be "rocky" but it is hard to tell because we cannot see through the layers of cloud and gas. The composition of the rocky core is also rather dubious, the pressure is very high, high enough to make predictions difficult. Above the center of Jupiter is a layer of liquid metallic hydrogen, made possible by the massive pressure. Above the liquid hydrogen is gaseous helium and hydrogen, capped off by frozen ammonia clouds mixed with some other chemicals. Because of the nature of gases, the boundary between liquid and gaseous hydrogen is not very well defined, they smoothly transition into one another.
Jupiter is surrounded by multicolored bands of cloud. Under each band of clouds, the wind is blowing the opposite direction of the surrounding bands. These winds are very fast, and so there are vortices and massive storms at their borders. The color of these bands is determined by the altitude of the clouds, blue being lowest followed by browns then whites with reds being the highest.
It was thought that Jupiter would not have rings orbiting it like Saturn, but during observation such rings did appear. The rings orbiting Saturn are largely ice, but Jupiters are dust. The magnetic field of Jupiter and the massive gravity probably slow the dust quite a bit, causing it to fall to the planet. The rings have managed to exist, however, because they are constantly being replenished by dust from impacts on the many moons orbiting the planet.
Jupiter is almost a failed star. The composition of the planet's atmosphere is very close to that of a primordial solar nebula. Through compression Jupiter is able to radiate more heat than it absorbs from the sun, its internat temperature reaching about 36,000K, not quite high enough to create fusion. Brown dwarf stars are even measured with respect to Jupiter, using Mj, or Jupiter masses.
Of all the planets in our solar system, Jupiter dominates. Most people recognize Saturn because of its rings, but Jupiter is by far the king, standing out in almost every way possible. Its mass can rival that of stars, and its magnetic field dwarfs all other planets. Jupiter truly is the king of the planets.