It's meant to be a tool where you can search for things to find out its popularity. Using the "Search for new keywords using a phrase, website and category." In the "Your product or service" textbox is where you will be doing all your searches.
Let's say I've been playing and recording a lot of footage of "Megaman 2". Let's search and see how popular it is... about 6k a month. Not terrible, but not great if I want subs. Let's try "Overwatch" 2.2 million... still not that great. Maybe let's try... "Pokemon"... 7.4 MILLION! Yes, make a video about that.