Here you can download the Pokémon GO app for you iPhone, iPad, or iPod Touch (iOS devices). You can even remote install it from you Macbook or iMac! There are optional in-game purchases available, but the app itself is free to install and play. The game requires 193MB of free space on an iOS 8.0 or later device. GPS is not required, but it will improve the playing experience significantly. iPhones are preferred over iPads
Here you can download the Pokémon GO app for you Android devices. You can even remote install to you phone or tablet! The app itself is free to install and play, there are OPTIONAL in-game purchases available. To install the game you need a device with at least 2GB of RAM and running Android version 4.4 or higher. While GPS is not a hard requirement, it will make playing easier and
Niantic Labs are the creators of the Pokémon GO app, and they have a subsection of their site dedicated to it. Here you can see some cool updates about the app itself, like it being released in other countries! You can also submit a support request or look through the FAQs.
There is lots of good info on the official Pokémon GO website: http://www.pokemongo.com/ You can find out about all sorts of stuff in the game and get some good, high-level info. It’s also the first place to have the trailer (aside from YouTube):