Cow Punching (Kellett Cattle Company)
Gain access to this mission by claiming the Kellett Cattle Company, in John's territory, and talking to the emergent quest giver.
Walk east, past the grazing cattle.
Rocks are the easiest way to get the cattle moving. Use as many as you need, but make sure they're running in the right direction.
Note that you don't have to get them to go through the gate- they'll happily blow clear through the fence, and the mission only depends on them standing in the pen at the end.
Herd all three in to complete the mission.