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?