To a brand new rider on a school master? Right rein to go right, left to go left, squeeze to go, pull and sit back to stop.
To a rider of a high level. Inside leg pushing to the outside rein for collection, get the inside bend by lightly using the inside rein, and turn the horse's body with the inside leg while regulating the size of the turn with the outside balancing aids. The outside leg keeps the impulsion from behind. Both legs are pushing the horse up into the connection and lifting the ribcage and rounding the back for proper engagment of the hindend.