This is the 13538th most frequent Russian word.
наступлением
"Наступлением" - "offensive," "advance," or "onset" depending on context.
Here, 'наступлением' is used in the sense of the coming or beginning of a new time period, 'весна' (spring).
С наступлением весны многие звери просыпаются от спячки.
With the advent of spring, many animals awaken from hibernation.
In this context, 'наступлением' refers to the commencement or start of a specific event, 'учебный год' (academic year).
Мы готовимся к наступлению нового учебного года.
We are preparing for the beginning of the new academic year.
Here, 'наступлением' is employed to denote an offensive or advance by the enemy, used militarily.