Question

what is desert how desert formed

Answer 1

Moist warm air rises over the land, deposits its water content and circulates back to sea. Further inland, areas receive very little precipitation. The Thar Desert near the India/Pakistan border is of this type. In some parts of the world, deserts are created by a rain shadow effect

Answer 2

Moist rising air near the Equator cools and condenses into clouds and, later, rain. As the current of air moves toward the pole, the air releases much of its moisture. By the time the current turns back toward the Equator, the air is descending. It becomes compressed and warmer, and its relative humidity falls further. Under these conditions, it is rare for clouds and rain to form. Add in a bit of wind to accelerate evaporation at the surface, and the continental regions below become extremely arid owing to the lack of available moisture. Deserts thus become dry.