I don't think it's available from the Mac App Store - use www.zoom.us and click the resources link then download client. This may work for the iPad too but it may well be available on the iOS App Store.
Thanks Mick. There is a zoom app on the app store for IOS, so I'll start there. If the screen proves to be too small, I'll follow your instructions for installation on the Mac.
Richard
Ironic that it's the Zoom thread that throws an error every time I try to comment. I had to remove an emoji from the post above before I was able to make it stick.