There are five core doctrines (teachings) that all Christians must believe. I (Alex) came up with an acronym years ago to make them simple to remember: IVDAR

Each of the letters stands for a doctrine of Christianity.

I — Inerrancy of Scripture

V — Virgin Birth

D — Deity of Christ

A — Atonement

R — Resurrection

For detailed information on each the five doctrines, and to learn about a sixth core doctrine that all Christians should believe, read: What is IVDAR? Or IVDARR?