Aztec worshiped many, many Gods.
The most important was perhaps Teotl (whose name also just means "god"). Another important God was the God of rain, Tlaloc.
They believed that the Gods required human sacrifices, which they performed in their temples - the sacrifice was their mayor ritual.
They also believed in afterlife, for example women who died in childbirth would after death fly towards the sun in the form of humminbirds. Depending on the form of death, afterlife had different forms.