As the name suggests, Google Trends shows you the trends of the various searches happening on the web. It is not the keyword suggestion tool, but you can use a keyword suggestion tool combined with Google Trends to know exactly for what keyword or keyword-phrase you should search engine optimize your content. How is that?
If you look up for a particular search term Google Trends gives you a numeric as well as graphic presentation of how many people are searching for this particular search term, how it fares compared to other similar search terms, during which time periods the search for this particular search term peaks, and so on. This way you can find out what keyword to target for.
The writer gives a very nice example of “car parts” and “auto parts”. Doesn’t “car parts” look like a good keyword to optimize for? Americans, on the other hand, use “auto parts” more, compared to “car parts” so you should focus on “auto parts” if you are selling products under this category (in America, of course). This you would not know easily without Google Trends. The article reviews many more features that you can use in order to improve your search engine rankings.