Sumerian religion is what people who lived a really long time ago in a place called Sumer believed in. They thought that there were gods and goddesses who controlled things like the weather, the sun, the moon, and animals.
They also believed that these gods and goddesses were responsible for how their daily lives went. For example, if they had good crops or caught lots of fish, they thought it was because the gods and goddesses were happy with them. But if something bad happened, like a big storm or fire, they thought it was because they did something wrong and the gods and goddesses were angry with them.
They had lots of different gods and goddesses that they worshipped, and they had special temples where they would go to pray and make offerings to them. Some of the most important gods and goddesses were An, the god of the sky; Enki, the god of freshwater; and Inanna, the goddess of love and war.
Sumerian religion was a big part of their everyday lives, and they spent a lot of time and effort trying to make the gods and goddesses happy. They even had special priests and priestesses who were in charge of making sure the temples were clean and that the offerings were given to the gods and goddesses.
So, in short, Sumerian religion was a belief system that ancient people had in gods and goddesses who controlled important parts of their lives, and they did lots of things to make these gods and goddesses happy.