Before buying EOS, you will need a place to store it. This is what a wallet is for, and it consists of two elements: a private key and a public address. A wallet requires a private key, specific to the individual, that enables access to the EOS address stored in the wallet, which is also the public key. The wallet is what enables EOS, or any cryptocurrency, to be a secure medium of exchange. Essentially, people can send EOS to certain wallets using the public key, which only the individual can access with their private key. Some individuals choose to keep their coins in their wallet provided by their cryptocurrency exchange, due to the fact that a lot of exchanges have mobile apps that allow people to easily buy, sell and spend cryptocurrencies.