What are Christian heresies? They are FALSE teachings that CONTRADICT the core teachings of the Bible, per what Scripture teaches about God, His nature and attributes, Jesus, the Holy Spirit, The Trinity, about sin and salvation. Note that various heresies and false teachings go back to ancient times. And some are found in churches today, disguised as TRADITION. To avoid heresies and whatever associated false misconceptions and dangers, it truly helps to first know what they are and WHY they are heretical. And so, here they are all are listed, in this amazing short video that identifies and explains why each is a heresy:
https://www.youtube.com/watch?v=D8s2TDoSc00
And here is a good reference to Biblical passages that warn us to avoid heresies, false teachings and teachers:
https://www.gotquestions.org/heresy-definition.html