Here is the part after you purchase. If you get stuck at any point down the road, don't worry! My only job is to help you out get up and running.
First thing first
(Mandatory) Make sure that node and npm are installed on you computer. It's a very simple step. Just go to https://nodejs.org/en/ download the package that's recommended for all users.
(Mandatory) make sure to install expo-cli on your computer globally by running:
npm i -g expo-cli
(Mandatory) Unzip the app folder you received on your email or clone the gitstrap repo you received by following the nativebase.io instruction.
(Optional) We recommend you use VS Code as coding environment and again "you don't have to if you don't like it."
If you have it or you do like to use it, however, I recommend you install the following VS Code extensions for better experience. (these extensions have nothing to do with the app at all, they are just good for coding experience in VS Code IDE)