This is the 1096th most frequent Russian word.
сентябре
"Сентябре" means "September" in the prepositional case in Russian.
This sentence uses "сентябре" in the prepositional case to indicate time (when an action occurs). It specifies the time period within which the natural events occur.
В сентябре природа начинает менять свои краски.
In September, nature starts to change its colors.
Here, "сентябре" is again used in the prepositional case related to the time frame of an event—her birth month.
Моя сестра родилась в сентябре.
My sister was born in September.
In this example, "сентябре" describes the designated time for the planned meeting, emphasizing the starting point of an occurrence (indicated by "в").