From a normal Squared Set (or from a Circle of alternating Boys and Girls).

Four Girls right-hand star 1/2 to the opposite boy, who Courtesy Turns them.

Ends in a Squared Set.

Four Ladies Chain       before   after Girls right-hand star 1/2   after Boys turn the Girls (done)

A verbose description:

Four Girls right-hand star 1/2 way across to the opposite Boy, giving the Boy their left-hand. Boys take the Girl's left-hand in their left-hand, then (Boys) face left to place their right-hand on the Girl's lower back. Boys backup to the left, turning the Girls about 3/4 (270°) to end in a Squared Set. The pivot point is between the two dancers -- Boys backup while slightly pushing the Girls with their right-hand.

See also Two Ladies Chain [Basic]