First you need either Creative or Professional version of Terragen.
Since scripted animations are too difficult inside the newer versions of Terragen now, like using Terranim or Camera Path Editor....some export the heightields and go to animation in other programs. Those old programs were quite simple to use, even for me; and the graphing elements gave a smooth camera view imho.
I have Creative version and think it well worth the cost just to play or experiment. Professional use may be another matter, but I do this for hobby only.
Many post results on YouTube or Vimeo, One Drive share or even DropBox dlld.