MetaMask is a popular cryptocurrency wallet and decentralized application (DApp) browser extension that enables users to securely manage their digital assets and interact with blockchain-based applications. To log in to MetaMask, you need to install the extension in your web browser, create a wallet, and set a strong password. Once your wallet is created, you can log in by clicking on the MetaMask icon in your browser, entering your password, and accessing your wallet to view balances, send or receive cryptocurrencies, and engage with various Ethereum-based DApps, making it a versatile tool for blockchain enthusiasts.