How are lasers used to determine the distance from earth to the moon?

A beam of laser is directed at a reflecting surface put on the moon when the beam of laser is reflected a receiver on the each measure the time since the beam was sent till it was received. Laser is simply light so it has constant velocity in vacuum ~ air (c = 3 x 10^8 m/s)

to find the distance:

t : time measured between launching the beam and receiving it

d : distance

d = ct