The same way: Viro kaj virino dancas.
If you want to be explicit about the continuous aspect, the fact that they are dancing right now, you can also say Viro kaj virino estas dancantaj, but the continuous aspect is used less in Esperanto than in English and is not mandatory.
I suppose the question comes to how Esperanto forms general constructions, that is to say, men, women, dogs, whatever in general. Is it like English where it's plural without an article, Spanish where it's singular with the article, or perhaps some other variation of singular and plural and article or lack of article?
Then what magic is needed to divine when to use it?
A knowledge of English grammar.
Which we assume that everyone who takes a Duolingo course labelled "learning ... from English" possesses.
I didn't add the a's because there were no la's,
la is "the", not "a".
Esperanto has no equivalent of "a".
I don't think this is correct grammar in english. It sounds like they're describing a type of dance - a "man-and-woman-dance". "A man and a woman is dancing" would be the correct way of saying it in english, no?
Is it only written in this way to teach us that Esperanto treats "a man and a woman" the same way as "they" gramatically?
Viro is always "a man"?
viro is one of Esperanto's comparatively-few strongly-gendered words: it always refers specifically to a male adult human being.