The example Google gives is a search for Taylor Swift. When you type that search term in, you'll want to pay attention to the subheadings in the search results that drop down; "American singer-songwriter" is what you're looking for. When you click on that search, you'll get a page that shows the search interest on that term in the US for the past week. If you want to dig past web-only search interest, click on the button at the top right (which defaults to Web Search) and choose Image Search, News Search, Google Shopping or YouTube Search. In addition to finding out the search spikes around specific events and videos, for example, you can also see where search interest is strongest for your chosen topic and platform.