"How about " is used to suggest something: " "How about a cup of coffee?" "What about " is asking about what you feel,know or think concerning something in particular . "What about him?" "What about last night's event?"

"How about? " is when you´re offering something (including an idea). Examples: How about some water? How about trying something different? "What about? " would be the similar to "what´s the deal with? ? " or "what´s with?". What about caffeine being bad for us?= What´s the deal with caffeine being bad for us?= What´s with caffeine being bad for us?

'How abou't and 'what about ' are both used to make suggestions. 'How about/What about going to the cinema tonight?' They are both used to make offers (informal) 'What about/ how about a cup of tea?' If the offer is a complete sentence you use 'how about' before subject plus verb.'how about I make you a cup of tea.' and 'what about' before participle. 'What about making a cup of tea' (but this is more like a suggestion) They are both used to ask someone the same question they have just asked you. 'How are you?' I'm fine thank you, what/how about you? They are both used to ask a question after a positive statement. 'I'm hungry, what/how about you?' 'What about' is also used to ask someone what they know, think or feel about someone or something. 'What about him?' (What do you know, think, feel about him?) but this is usually part of an ongoing coversation the topic of which is already known to the speakers.