Ask "how about ___?" to suggest a choice:
A: What should we eat tonight?
B: How about pasta?
You can also use "What about ___?" in the same way.
Another way to use "How about ___?" is to suggest an action:
How about we stop arguing and start coming up with a solution.
"What about ___" doesn't work as well in this case.
"How about ___" is a casual phrase.