In July 2019 we lost 870 square miles of the Amazon to deforestation. This clear cutting of the trees has lead to less moisture in the air and as a consequence makes the whole rainforest more susceptible to fires.
Wildfires in the Amazon happens (sadly) every year. In part due to the dry season and climate change, in part due to humans. Organizations do this to clear space for mining, drilling and cattle ranches (to name just a few). The Brazilian government has been expressing a huge disdain for the rainforest, downplaying it's importance, it's biodiversity and rolling back measures to protect it to give more land to logging companies and the like.
It's also so important to point out that naturally occurring wildfires have actually been shown to help forests worldwide, as they clear dead trees and some seeds actually need the heat in order to germinate.
Be angry that the Amazon is on fire. But be much more angry, much more afraid, much more appalled at the fact that humans are intentionally doing this for money, for greed, without a care to the climate crisis or biodiversity loss.