Spotify is already on the iPhone but we don't pay much attention to it because we carry it in our pockets so we don't get to notice what Spotfy has to offer. The iPad app is different because it gives you the cooler thing offer your home stereo, which benefits the High Def album art that uses it's Retina display.
What Spotify offers you is that you can connect wireless with the Airplay or Bluetooth function on your iPad. So if you have any speaker connected with Airplay or Bluetooth you can enjoy this app. Or if you just want to enjoy the speakers on your iPad you can do that as well. But it is better if you enjoy it with you on a workout or if you want to throw a party. It is up to.
The app really uses the iPad's 9.7 screen look really cool where as the iPhone and Android don't offer that. You can create your own playlists or select the artists that you want to hear. It is somewhat similar to Pandora but it is way more cooler. Spotify has posted a video on YouTube where you can see what the app does especially the feature where if you don't like the song that you are listening to you can just swipe the album art and change into another song.
While the app is available for free you need to take full advantage of the app by purchasing the subscription plan which is known as Spotify Premium. You can try the app for free for up 48 hours and then after that you can try a 30 day trial version and then go with the subscription. I recommend it.