Can somebody give me examples of religion's beliefs that directly conflict another religion's? Things like monotheism and polytheism.

Catholics and Lutherans- Transubstantiation vs Consubstantiation, respectively. Transubstantiation is the belief that the Eucharist really does become the flesh and blood of Christ, while the Lutherans believe it's symbolic.

They also differ in their belief of good works vs. faith in Jesus as paths to salvation. Catholics believe that good works pave the path to Heaven while the Lutherans believe that God acknowledges that humans are sinners so the real path to Heaven, according to them, is paved with faith in Christ.

Correct me if I'm wrong on minor accounts- I'm not religious at all, I just remember these things being taught in my history 1 class during the reformation.