Your POA Network investment is looking to build apps on top of the native Ethereum chain, only faster and cheaper. They do so by utilizing their offshoot as a side chain of the main ETH chain. This process reduces cost and increases speed and security.
Their platform is looking to solve the largest problem with the Etherum chain: scalability. They run on their very own algorithm called Proof Of Authority where block validators must go through a verification for the privilege of securing the blockchain.
They have the advantage of already having a working product, but I do have some concerns that Ethereum's upcoming Plasma network may render their solution obsolete based on the fact that their big brother has such a huge lead on them due to ETH's overwhelming market share, and the fact that many apps, even this one are already using the system in question.How to buy?
You can buy POA Network on at least one top-five exchange and a couple smaller ones as well. The Bitcoin trading pair holds most of the volume for this coin, but there is some liquidity for Ethereum as well if you would prefer to make your trades in this manner.
This is an ERC20 token, and that means you can store it in any wallet that will accept Ethereum style assets. There are lots of options for this, but if you need a suggestion then consider My Ether Wallet, Meta Mask or a Trezor hardware wallet to keep your investment in a safer cold storage type of solution.