I am pretty confused with the keyword analysis, Which set of keyword should I target exact or broad. What is the difference here?
You must use exact as your reference in finding good keywords. Exact keywords means "the exact words which people are searching in search engines" while broad keywords means "some of those words are part of the exact keyword that they are searching". I hope you get the thought.
Broad match will substitute similar words. You can narrow down the results from google's keyword tool by unselecting Broad Match to be returned in your results. Currently, its on the left midway down the page after you search and get your initial result set. Unchecking starts removing results.