Vue Pro studio 7 Mac. I looked in the docs but could not find out how to save a terrain I have created not for export but for re-use in Vue. Thanks for your help.

Just save it normally, as you would save any normal object (right click -> save object). When you reload it in Vue, it will know it's a terrain and will treat it as such.

Where would you save it in what folder? Or should I create a new folder?

That doesn't matter, you can save it wherever you like. Same goes with anything else you save. I would only advise to have a separate folder for your own objects so that you don't lose them if you uninstall and reinstall Vue.

Thank you