together with; as X, then Y (e.g. as we age we gain wisdom, as wine matures it becomes more valuable, etc.)
時代と共に価値観が変わる。
Values change with the times.
成長と共に責任も増えます。
Responsibilities increase with growth.
彼女と共に新しい生活を始めた。
I started a new life together with her.