There are differing schools of thought regarding the vast amount of deities in Hinduism. One school, which is what most outsiders are aware of, is that each god is individual from one another and they have varying domains, powers and relationships, much like the ancient Roman and Greek gods. Another school suggests that all of the different gods are expressions of a singular God, much as how Christianity has the Holy Trinity who are three separate beings (Lord, Jesus, Holy Spirit) that are also simultaneously one being.

You’ll find that oftentimes outside of the context of a puja or a religious holiday Hindu people will often just refer to ‘God’ rather than a specific deity e.g. “Thank God” rather than “Thank Durga” or “God is watching over you” and not “Ganesh is watching over you”. I’m not sure if this reflects their school of thought on mono/polytheism or is just language simplification, but from what I’ve gathered from Indian communities here in Australia the ‘many gods; one God’ idea seems to be pretty prevalent.