Light is fast, but not instant. In empty space it travels at exactly 299,792,458 m/s, about 300,000 km/s (this value defines the metre). In one year it covers

299,792,458 m/s × 31,557,600 s ≈ 9.46 × 10¹⁵ m, or about 9.46 trillion km.

That distance is one light-year (ly). It is a unit of distance, not time. A star "ten light-years away" is a star that is 10 × 9.46 × 10¹⁵ m away.