GNT is distributed supercomputer that allows anyone to use its resources at a much lower cost than they would be purchasing their own equipment. This computing power can be used for scientific research, data analysis, graphics rendering, machine learning, AI, or anything else that could require a large volume of computing power.
It also allows users to earn tokens via the sharing economy by allowing anyone to contribute their CPU power to the network. A Golem investment also provides resources for developers to host their services or apps on a decentralized environment with zero downtime, a cheaper cost than running their own server and immunity to DDos attacks.
You can buy Golem on many exchanges. Their volume is pretty evenly distributed which means you'll be able to get a fair market price pretty much anywhere you decide to buy your tokens. The most popular trading pairs are for Bitcoin or Ethereum.
GNT is an ERC20 token, and so you can store it in any compatible Ethereum wallet. This means you can use any wallet that allows the storage of Ethereum assets such as My Ether Wallet or mobile wallet Coinomi. It's also possible to use a hardware wallet that accepts these tokens should you wish for more security for your investment.