Trouble understanding Braintree integration into Android

I've read through the docs on http://ift.tt/1GrDpnH and I'm having trouble understanding what to do.

As I understand it, we must build a server to generate a client token which Android Studio then deals with. What I don't understand is how to build the server to generate a client token with each request, along with generating customers and updating customers.

I'm relatively familiar with Ruby, and I know that Sinatra is a good way to host servers with Ruby knowledge.. but can anyone lend some sort of clarity on what are the steps to going from no server to accepting credit card details?

Another confusing aspect is that some blogs say that using Braintree is as easy as copy/pasting a few lines in Studio, and others say that you have to build your own server. Anyway, please let me know your thoughts!