Gas giants are commonly described as lacking a solid surface, although a more accurate description is to say that they lack a clearly-defined surface. Although they have rocky or metallic cores - in fact, such a core is thought to be required for a gas giant to form - the majority of the mass of Jupiter and Saturn is hydrogen and helium. In the planet's upper layers, these elements are gaseous, as they are on Earth, but further down in the planet's interior, they become compressed into liquids or solids, which become denser toward the core.
Some Uses of gas giants
Gas Giants are very common within the universe. The Ancients used these for technological devises such as Potal raft field barriers and as Prision Shafts for such beings as the Precursors one paritcalar gas giant (being a hot jupiter) named JK-191067 was used as a Relocation-map devise however many more may serve the same purposs.
Humanity used the planet jupiter as a hydrogen harvest.