This is the 38th most frequent Hebrew word.
שלנו
"שלנו" means "ours" in English.
Here the word "שלנו" is used as a possessive pronoun to indicate that the book belongs to us collectively.
הספר הזה הוא שלנו.
This book is ours.
Here, "שלנו" is applied similarly as an adjective to indicate possession, referring to "הקבוצה" as the team belonging to us.
הקבוצה שלנו ניצחה במשחק.
Our team won the game.
In this instance, "שלנו" is used as a possessive adjective associated with "הגן", showing that the garden belongs to us.