It is convenient to think of the distances to the stars in terms of the travel time of light. In one second of time, a light beam will travel about 186,000 miles. It takes sunlight about 8 minutes to reach the earth from the surface of the sun and about five and one half hours to travel out to Pluto. Thus a light beam would require more than four years to travel from the earth to Proxima Centauri. It is inconvenient to measure the distance to the stars in miles, because the numbers are so large.
Astronomers therefore use a larger unit to measure stellar distances.
This corresponds to a distance of 6 trillion miles. In these terms we would specify the distance to Proxima Centauri as about 4.2 l.y. The stars lie at varying distances away from us. Sirius is for example at a distance of 8.7 l.y., while Procyon is at 11. Many stars lie vastly much farther away.