The quick tutorial when you first open the Google Search app shows you how to effectively use Google Now's features.
When searching for well-known places or people, Google Search returns vital info up top. Also, notice the toolbar on bottom that lets you swap among different types of search results.
With Google Now, the Google Search app can understand natural language queries.
With permission, Google Now can look at your search history, e-mail, location, and other data in order to serve you cards with important information.
Google Now cards can even take information like flight itineraries in your e-mail and give you a card to remind you of your flight schedule.