"combine personal information from one service with information, including personal information, from other Google services"
For example, when you’re signed in to your Google Account and search on Google, you can see search results from the public web, along with pages, photos, and Google+ posts from your friends and people who know you or follow you on Google+ may see your posts and profile in their results. You can also find relevant information from the content you have in other Google products that you’re using, like Gmail or Google Calendar.
If you’re planning a trip to Italy, and you search for "florence" on Google, you may see photos or articles from your friends about Florence in your search results. These results make it easy to explore their recommendations and strike up a conversation about which sights to see. Learn more.
Google Now uses data that you may have stored in other Google products. For example, if you have searches stored in your Web History, Google Now can show informational cards based on sports scores, flight status, and so on, based on those past searches. To manage your Web History, visit google.com/history/. You can delete or pause your Web History and still use Google Now, but certain kinds of information won't show up. Learn more.
If you have a Google Calendar entry for a business appointment, Google Now can check traffic and suggest when to leave to reach your appointment on time.