When dealing with cryptocurrencies or crypto assets such as Ether and ERC20 tokens, it is crucial to always be aware of and have your private keys, mnemonic phrases and passwords backed up in case the unexpected occurs.
When you create a new MetaMask account, you are prompted to accept two screens concerning privacy and terms of usage followed by a page where you enter a password. This password is what allows you to unlock your local MetaMask account as it's installed. However, if your computer crashes or if you are somehow unable to access your MetaMask account while it's unlocked. This password will not help you gain access to your funds from another machine or after a crash.
The following page where you are given your 12 word seed phrase is the most important bit of information for you to record and keep safe when managing your MetaMask account.
You can write your seed phrase down on a piece of paper, store it on a flash drive or we also make it optional to download a file containing this information.
If for some reason you forgot to record your 12 word seed phrase or you lost the original copy, as long as your MetaMask account is still unlocked, you can reveal your seed phrase so you can back it up again.
Drop Down Menu > Settings > Reveal Seed Words (then follow instructions)