Once you've clicked on the link, the help on the left of the screen can explain this tool better than I can. What I can advise is the following:
Choose words and phrases that are "low" in the competition category
Choose words and phrases with between 50,000 and 150,000 global monthly searches
By keeping these parameters in mind, you'll ensure that you'll be found (less than 50,000 global monthly searches and you won't be on the 'map' and more than 150,000 the competition will be so great that you'll become a 'needle in a large haystack'). Give it a try and see if you can increase traffic to your blog and your website and increase business. Take it one step further and use your keywords at the beginning of a sentence or the end of an article/sentence/paragraph!
This is also a tool I plan to use when writing for Ezine as well - and best news yet? It's FREE - now that's a price we can afford no matter how small or large our business is!