I've been watching a lot of documentaries on the Roman empire and am curious about Roman religion during those times. I'm interested not in the mythology and stories (ie Jupiter is the god of the sky or whatever) but rather how the people of the time worshipped those gods, what kind of rituals, which gods did they worship, where and how was this done, etc. And I understand this likely changes many times throughout the history of the republic/empire. I hope my question makes sense.
Gradel's Emperor Worship and Roman Religion (2002) is quite a good starting point, explains how the Imperial Cult and how religion was approached in the Roman Empire since it's a very different approach compared to other modern religions
You might like the Companion to Roman Religion, edited by Jörg Rüpke (Blackwell, 2007). It has chapters by various authors concerning historical background, contexts/media, symbols and practices, actors and actions, identity, and perspective. It is a bit expensive on amazon at the moment, but you can probably get a copy via interlibrary loan from your local library/institution.