Pretty much everything else like selling on eBay, Amazon, affiliate marketing, blogging and making money from a website ALL need great keyword knowledge to make money - unless of course you want to pay vast sumes for advertising - forever!
So which keyword tool should you use?
I would go for one that shows you the DEMAND of any given keyword, the SUPPLY of that keyword (ie how many other people are already supplying information using that keyword) as well as KEYWORD IDEAS.
You want to use keywords, ideally, that have a good demand and low supply so you have a chance of getting traffic for those keywords.
Go here for Keyword research and spy tools
Don't underestimate the importance of keywords if you want to make money online!