Why do you have weather - what is it?

Because there are 4 seasons. And seasons are because of the earth's rotation around the Sun. Basically, what matters is the number of sunny hours. If you live on the Equator, there is only one season and the weather is very much the same throughout the year because it gets constant sunlight. And within seasons weather changes due to earth's rotation around its own axis, there is condensation cycle as well, so it is pretty complex in nature.