This is the 181st most frequent Hebrew word.
בתחילת
At the beginning of.
Here, "בתחילת" denotes the starting point of the movie in time.
בתחילת הסרט, הופיע הקדמה קצרה.
At the beginning of the movie, a short introduction appeared.
In this sentence, "בתחילת" expresses the time shortly after the meeting commenced.
הוא נרדם בתחילת הפגישה, וכך פספס מידע חשוב.
He fell asleep at the beginning of the meeting, thus missing important information.
The term "בתחילת" is used to indicate which part of the book is being discussed, specifically the introduction phase.