A forest is a piece of land with many trees. Forests are important and grow in many places around the world. They are an ecosystem which includes many plants and animals. Many animals live in forests and need them to survive.
Temperature and rainfall are the two most important things for forests. Many places are too cold or too dry for them. Forests exist from the equator to near the polar regions, but different climates have different kinds of forests. In cold climates conifers dominate, but in temperate zone and tropical climates forests are mainly made up of flowering plants. Different rainfall also makes different kinds of forest.
There are no forests in deserts, just a few trees in places where their roots can get some underground water. Aquifers beneath the Sahara desert have plentiful water, and also beneath Australian desert areas. The general term for this is "groundwater".