The Google Apps (also called as GApps) are the proprietary applications by Google included in many Android devices. Most of the applications can now be found and updated via the Google Play Store.Some of the apps include the Google Play Store itself, Google Talk, Google Sync (for adding and synchronizing Google accounts), Google Backup Transport, Car Home, Gmail, Google Maps, YouTube, Google Search, Google Voice Search, Google Music, and Google Docs.
In case you are having core Android or OEM version of Android, these are included or you can install it from Google Play. In case you are having a custom ROM, you might need to install them separately as they are not included in the custom ROMs as mentioned by Google. So if you run a custom ROM here are the links to download GApps.
1. Jelly Bean (4.2)
2. Jelly Bean (4.1)85785874558457845158412
3. Ice Cream Sandwich (4.0)
4. Gingerbread (Android 2.3.x)
5. Froyo (Android 2.2.x)
If you are looking for Android USB drivers, you can check them here.