In informal English, what about and how about
can be used at the beginning of a question. They mean the same thing.
What about Sally? = How about Sally?
In these sentences, the speaker wants to know something more about
Sally, in the context of a conversation already taking place. The speaker
might also say: "How does Sally feel about this?" (topic already
under discussion), or "What happened to Sally?" (topic might
already be under discussion), or "How did Sally do on the exam?"
(besides the other students already mentioned), for example.
In addition, what about and how about,
used at the beginning of a question like these below, are an informal
way of making a suggestion:
What about seeing an early movie tonight?
How about seeing an early movie tonight?
In these two sentences, the speaker wants to know how the listener
feels about seeing an early movie tonight. The speaker could also say,
for example: "Do you want to see an early movie tonight?"
or "Let's see an early movie tonight, shall we?" or "I'd
like to see an early movie tonight—OK?"