Reply to Traktor iPad version Or any other iPod apps

I'm slightly confused on how this app works

Does this just take songs from your Apple playlist that you've downloaded and enable you to mix them through this app. Is it a case of just picking two songs and pressing go on the song you want to mix into the song playing and the software matches them up to enable the mix to be carried out whilst performing some loops n other effects?

Or am I totally misunderstanding what is capable of this app.

Also can I connect this up to the same Soundsystem That my decks and mixer setup to?
Or does this only play over the iPhone speakers or iPad speakers?

I'm really not up to date with technology lol but Would like to incorporate my iPad into my basic setup which is turntables and an average Joe Mixer?
Any help or suggestions would be amazing