Polytheism is the worship of many Gods, traditionally clustered into pantheons. A person who worships many Gods is called a polytheist.
The word polytheism can be used to describe many religions. Some polytheists prefer not to use that term for themselves and instead use a specific term related to their religion, as the word has been stigmatized by evangelical missionaries who try to equate polytheism with “primitiveness” to shame people into converting. Others may prefer to emphasize what their religion is about without using a contrastive term, as polytheism is contrastive with monotheism.
Polytheistic religions usually:
Have a set structure or ritual language for how Gods are worshipped;
Allow for multiple philosophical systems and theologies, usually clustered into schools;
Have complex, multi-layered connections with the societies that practice these religions; and
Contain rich, multi-layered myths and commentaries about these myths that have developed throughout the history of the culture(s) in which a specific pantheon is worshipped.
Often, myths with immoral elements are critiqued within the commentary tradition, just like similar stories in monotheistic religions; as examples, see polytheistic philosophers' critiques of traditional Greek religion in the early Common Era (for the Platonists, every God is good) or the many exegetical conversations about Gods' myths within Hinduism.
While pantheons often include one or more leader deities, the relationship of that God (or Goddess) to the remainder of the pantheon can vary depending on the religion.
To learn more about polytheism (and specific polytheistic religions), try one of the following sets of search terms:
polytheistic theology
NameOfReligion theology "Gods"
philosophical interpretation myths NameOfReligion
theological commentary myths NameOfReligion
NameOfReligion ethics
NameOfReligion schools of thought
Good luck with your investigations!