The Aztecs believed in many gods.
Some of their gods controlled nature. The Aztecs believed that different gods watched over their seeds and plants and harvest. Various gods were in charge of the rain and water and wind. These gods worked together (most of the time) with the god who actually produced food, the god Chicomicoatl.
The Aztecs believed that gods needed rest, just like people. There were two gods of war - one for wars fought during the daytime, and one for wars fought at night. That way, one god could sleep while the while the other watched over the Aztec warriors. Aztec warriors were ready to fight at any time because they believed one or the other of their war gods would be by their side.
The Aztecs believed their gods had families. Some gods were related to each other by blood or through marriage. For example, Quetzalcoatl was the god of civilization. He was a very important god, but not as important as his brother, Tezcatlipoca, who was one of the two Aztec gods of war. The other war god was named Huitzilopochtli.
The Aztecs believed in an afterlife. After they died, they believed they would be assigned a job to do that helped their gods.
The Aztec people took their gods very seriously. They believed their gods would punish them if they did not worship their gods every day. In fact, they believed they would be punished if they worshipped their gods every day, but somehow, in spite in their best efforts, did not worship them enough in the eyes of their gods. They were terrified of their gods and what they might do if angered.
That's why worshiping their gods was a big part of Aztec daily life, and why their priests were especially important in the Aztec culture. The priests told the people how to behave so they would not anger their gods.
All Aztec priests were religious leaders. Some were active in government. Some acted as teachers. Some created the many records the Aztecs kept, written in hieroglyphics.
Some priests conducted the many sacrifices needed to feed the hungry gods, to keep their gods happy. Both men and women were sacrified, but there were many more men than women. That's because a great many people sacrified were enemy warriors captured in battle. But if the Aztecs ran out of captured people to sacrifice, or in times of great despair such as famine, they sacrificed their own people.
The Aztecs built temples to honor their gods. Temples provided a place for the music of worship, a place for the private ceremony of personal bloodletting, and a place to conduct the many human sacrifices that the Aztecs believed were necessary to keep their gods happy. Some temples were huge structures. The Great Temple of Tenochtitlan could fit 8,000 people in its plaza at one time. Some were small shrines where priests went to talk to the gods to keep themselves on the right path.
Everything the Aztecs did, they did to honor their gods or to make their gods happy. They truly believed if they did not keep their gods happy, the world would end.