The site explains that one you begin to understand how it works, Cortana becomes an invaluable part of the browsing experience. It works in the background and brings up information when you need it. For example, when you click on a word you don't understand or want more information, Cortana will bring up a sidebar in your browser with extra information. Cortana is contextually aware, so if you read an article about Apple the tech firm it will not pull up information about the fruit.
Cortana can also be of great help when visiting sites of brick and mortar businesses, it will give you a quick notification that it has extra information, which can include hours of operation, reviews, directions and photos. Similarly, when you enter weather in the browser's URL bar, Cortana will pull up local weather forecasts in real-time.
The integration of Cortana into Microsoft's browser seemed weird at first but Neowin reckons it could be Spartan's killer feature:
Once you get used to Cortana in the browser, it is genuinely hard to go back to browsing without the personal assistant. The additional information layer that Cortana provides is not only useful, but it is provided right when you need it and exactly how you would expect it. While Cortana may at first have seemed like an odd addition for the browser, this could very well end up being Spartan's killer feature.Here's a screenshot of how the current test version looks:
And here you see the extra info Cortana provides when visiting a restaurant's website: