Basically, the property focus just chooses where the system should render first, the CameraSubject is what the camera follows. The documentation is your friend.
Script:
wait(5)
local cam = workspace.CurrentCamera
local player = game.Players.LocalPlayer
local FocusPart = game.Workspace.FocusPart
cam.CameraType = “Fixed”
cam.CameraSubject = game.Workspace.FocusPart
wait (5)
cam.CameraSubject = player.Charater.Humanoid