Connecting a custom gandi.net domain to Ghost (Pro) for the easily confused

The official Ghost documentation guide is plenty helpful - you can reference general instructions here - this guide is for you if the Record Type - Host - Value notation on the table confused you:

Access the gandi-specific instructions on this page and complete "Step 1"

If you too are confused and have no idea what the "Host" and "Value fields correspond to in the "DNS Record form", here's how it goes :

Name: www
Hostname: [yoursubdomain].ghost.io. (yes, the dot is essential!)