Metamask is a centralized wallet that works with decentralized dapp applications of the ethereum platform, it was created in 2016 for this, its creators used an ethereum web Api that is public, which is a library that allows creating web applications that interact with technology ethereum blockchain, with this they achieved that dapps could be executed in the browser without any problem. Initially they operated with Crome but later they released extensions for the rest of browsers. This wallet is already incorporated into some dapps such as: The Bit2MeDEx Exchange, the games CriptoKitties and 0xUniverso, The MyEtherWallet wallet and many more. Its installation is very easy, it is installed the same as you install any Chrome extension if you are going to use it there. Or extensions from other browsers. When installed, a wallet and its corresponding password are generated that can be remembered with a confirmation phrase. So whatever happened never lose your wallet, you can always get it back.