To start with there are many kinds of deserts. Some are the familiar ones with bare rock and shifting sand, upon which the hot sun beats down, but others, such as the Gobi, have bitterly cold winters. So a desert is a region where only special forms of life can exist and they have adapted themselves accordingly.
A good example of this is the cactus. This has adapted extremely well to hot, arid condition. They have thick, fleshy stems which store water. Little or no leaf surface prevents to much evaporation of water from the plant’s surface.
Many desert plants have thorns, spines, or a horrible taste and smell which discourages animals from eating them. Desert plants usually lie dormant during the dry or cool season, or drop seeds that can survive such s period.