If planets are made of gases how do they have land forms?

Answer 1

In our solar system, the outer planets, all referred to as gas giants, have no solid outer surface at all, their entire outer envelope is gas; any artifacts visible on them are attributed to local changes in composition or weather effects. Jupiter, Saturn, Uranus and Neptune are all believed to have relatively small solid rocky (silicate) cores, largely similar in composition to the inner planets. Note that due to extreme pressures there are phase changes, for example, on Jupiter there is a thick layer of metallic hydrogen around the core, then a layer of (supercritical) liquid hydrogen; this reflects the physical principle of the correlation of depth and pressure - moving outwards from the core you would note a gradual decrease or a gradient of pressure all the way out to a point where the distinction between the edge of the atmosphere and the beginning of empty space would blur somewhat.

Answer 2

Planets are not made entirely of gases; they have solid surfaces as well. The solid surfaces of the planets are typically composed of rock and minerals. The gases that make up a planet's atmosphere are separate from its solid surface.