MetaMask is a browser extension that bridges the distributed web of tomorrow to your browser today, so that the transition will be seamless. To be more specific, it allows you to run Ethereum decentralized applications right in your browser without running a full Ethereum node. MetaMask provides you with a secure identity vault and a user interface to manage your identities and sign blockchain transactions on different sites. You can install the MetaMask browser plug-in on Chrome, Firefox, Opera, and the new Brave browser.
More instructions on how to setup MetaMask can be found at https://minds.com/token.
You may also view this short tutorial if you wish to setup MetaMask.