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.