The Earth is the planet that we live on. It spins around the Sun, from which it receives most of the heat energy in the form of sunlight, within a year (365 days).
The Earth's atmosphere makes it a place that allows life together with the existence of humanity. Atmospheric conditions are different all over the world. These differences are called climate, and make living conditions for life very different (from "nice" over "hard" to "hostile") on various parts of the Earth.
Besides, atmospheric conditions often change daily. These daily changes are called "weather" and are the external conditions that we feel more immediately. This is why we often talk about the weather.