At first; during the initial period (when something has just begun), often implying a period of adjustment or learning.
初めのうちはミスが多いのは普通だ。
It's normal to make many mistakes at first.
初めのうちにルールを覚えておいてください。
Please learn the rules at the beginning.
初めのうちは難しく感じるかもしれないが、慣れれば簡単だ。
It may feel difficult at first, but it's easy once you get used to it.