Usage patterns
最初に〈動詞〉to do something first, as the initial step
First, please wash your hands.
最初から〈動詞〉to do something starting from the very beginning
Could you explain it from the very beginning?
最初は〈形容詞〉to be a certain way at first (before things change)
I was nervous at first, but I got used to it quickly.
Expressions
最初から最後までfrom beginning to end; from start to finish; all the way through