This is the 16612th most frequent Russian word.
секцией
"Секцией" (instrumental case of "секция") means "by/with a section" or refers to "a section" in a division or group.
In this sentence, 'секцией' refers to a group or department within a community or institution dedicated to swimming activities.
Я занимаюсь секцией плавания уже три года.
I have been attending the swimming section for three years.
Here, 'секцией' denotes a part or subdivision of a physical entity, such as a piece of furniture.
Шкаф был разделён на четыре секции, каждая с отдельной дверью.
The cabinet was divided into four sections, each with a separate door.
In this instance, 'секцией' is used to represent a specific part or division in a setting, such as a conference or organized event.