Beginning
In The Beginning, First Of All, To Begin With
expression
This is a time based word (because of the に). What is the first point of time when you are beginning something? That is the beginning.
This word uses the kun'yomi, which you didn't learn with the kanji, so here's a mnemonic to help you out. What are you beginning? You are beginning Haj (はじ). (Haj is the fifth pillar of Islam, and is a pilgrimage to Mecca during the month of Dhu al-Hijja).
花さんとは、4月の初めに出会いました。
I met Hana-san at the beginning of April.
うちは毎年、年の初めに家族みんなで朝日を見に行きます。
Our family goes to see the sunrise together at the beginning of each year.
初めに口を開いたのはカオルだった。
It was Kaoru who first opened her mouth.