What is belief system of Coptic Christians in Egypt?

I tried to research this online, but the articles coming up make vague statements and do not explain or give details about what is their beliefs regarding Christ and what do they mean calling themselves patriarchs in relation to Apostle Mark? Do they believe Mark will be reincarnated in association with Christ's return and come from their lineage? They reject notion of Christ having dual nature of divine and human, that he is only divine (according to the sources I read), what exactly does that mean since Christ was in human form? One article I read said the differences in belief about Christ they have with other Christian churches is "highly technical" and did not bother to explain any of it.