Then its same universal brotherhood ..i mean all mankind came from adam and eve and then get evolve into different nations, beliefs and races ..Its confusing as well because how can you be Hindu when you dont practice or take opart in hindu rituals/customs or traditions and dont consider bagvad geeta as holy ?
Well, the adam and eve story doesn't really withstand scientific scrutiny. Humans evolved from homo erectus.
For the second part of your post, I know it must be confusing to people who are schooled in the abrahamic faiths. Religion is a very different affair in the eastern religions. There are no single hindu rituals or customs. A hindu in Rajastan will have very different customs and rituals from a hindu in Kerala or Tamil Nadu.
It's not like there is one central book or dogma, like the quran or talmud. There is no single authority or practice. "Hinduism" was a term invented by the British, there is no "who is a hindu" and who is not. The hindu scriptures are all addressed to people in general, and you wont find the word "hindu" in any of them.