Safari's interface has changed quite a bit in iOS 7. There's a new, unified search bar at the top of Safari.
1. To search, just tap the search bar.
2. Type in your search term and tap the Go button on your onscreen keyboard.
Safari will display search results from your default search engine.
I've found that it's much better having the unified search bar. Previously in iOS 6, I sometimes found myself typing the search term into the wrong box. iOS 7 has made searching in Safari faster and easier.