Let say you have a keyword "webdesign".
Google will give you the total of how many times per month or yearly that keyword was search for.
Not only global but local also.
This way, you can create better keywords for you website and AdWords Advertising.
So, If you make use of a SEO-company,
make sure that they offer you this service, otherwise you will never know what keywords
are best for your company ad or website.