I want to use Survey Monkey to survey my demographic. How?

Well my friend, I congratulate you on trying to ask your customers first. However, this is still a very difficult route to go that will yield very little information if you don't spend money and time. For an outsider to gain market insider knowledge is extremely expensive. Let's say you find that one in 100 people like your idea. To access such a broad customer base would require 1 million dollars at least. While it is nice to target "any adult", it is too broad a segment. The right way is to niche down first and then scale.