follow mode will make the camera follow in the yaw axis when moving in either direction on the yaw axis and will stay fixed.
free mode will keep the camera where your cameraman or you left it while adjusting during flight so when moving you have to correct the way of the camera to the object you want to record.
fpv will lock the camera, yes so the pilote is able to see the status of th i1 in horzontal and vertical direction making it easier to fly since the pilot "sits" within the I1 while flying.
sorry my english, hope that helped.