Stuff like how Kylo feels about Vader’s turn and the relationship between the Resistence and Republic is in the film. It’s just not spoonfed to the audience though things like R2 waking should have been fully explained because it was a giant plot convenience.
EDIT:
Luke using a T-16 doesn’t fully explain how he was so good in a space battle. Flying an X-Wing is one thing flying in a dog fight is another.