No. App Store on iTunes only work on iOS devices (iPhone, iPad and iPod Touch). Nexus S has the Android Market built-in (it's the app store for Android phones) so you can get apps from there (most of the popular iOS apps can be found on the Android Market). The icon should be something like a shopping bad with the Android robot on it.
You can also download third-party app stores from all over the web. But, the most popular one is Android Market. You can also download apps directly from websites and put them in the phone (with a simple Copy+Paste).
You can also download third-party app stores from all over the web. But, the most popular one is Android Market. You can also download apps directly from websites and put them in the phone (with a simple Copy+Paste).