When to use βραδινό and when to use δείπνο ?
Δείπνο is more formal and can be used for formal dinners. πχ: επαγγελματικό δείπνο and not επαγγελματικό βραδινό.
Like dinner vs supper?
Yes, but δείπνο is always night meal. (contrary to english where dinner can be any formal meal, i think.)
In British English, the use of 'dinner' also varies by region. Most areas refer to the three main meals of the day as breakfast, lunch, and dinner, yet other regions use breakfast, dinner, and tea. :)