What is Pillar Payment Network and how does it work?

I was trying to use Pillar Network inside the iOS app, but I got a bit confused. The app forces me to create a Smart Wallet, which has a cost of around 20 US dollars. Before I proceed, I would like to understand: how does the network works in the details? I have read a few blog posts by Pillar which which I found in Google. But the explanaiton is very high level. Is there any documentation?