Google Adwords Keyword Tool
Google Adwords Keyword Tool allows you to build extensive, relevant keyword lists from one simple interface. Generate keyword ideas, review traffic estimations for existing and new keywords, and if you are using adwords you can add lists of keywords directly to your ad groups in one step.
Keyword Tools Basics
The Google keyword tool allows you to enter a keyword or the URL of a website. It will then provide a list of related keywords and display some search data to give you an understanding of how popular those keywords are within google.
Heres an example, enter the keyword "apples" and the keyword tool will provide you with a list of keywords relating to your search

As you can see, you can quickly produce keyword data for use in your ads and content.
Improve your keyword results
By analysing google's data you can quickly find niche keywords that might have a lower number of competing ads, therefore costing you less per click and driving very specific targeted traffic to your advert rather than a wide range of generic traffic that likely will not convert as well. Using our example of apples, you can work through your list of keyword alternatives and highlight potential candidates.

Remember, 100 clicks with a conversion rate of 10% is just as good as 1000 clicks and a conversion rate of 1% and actually cost you ten times less for the same amount of converted users.