Metamask is not just a wallet for the ether tokens. This is a special add-on that allows you to work with decentralized applications.
What is decentralized application? (dApp)
DApp differs from the ordinary application by the way using smart contracts of Ether.
Technically, dApp can use another blockchain (not ether) and not to use smart contracts at all, it’s a very broad concept. But at the time of writing this post, 99% of decentralized applications are services that use Ether and Metamask smart contracts as a bridge through which the user interacts with the smart contract.
It seems that it is difficult, but before the user had to run full ether node on his/her computer (today it takes about 700 gigabytes and requires settings) to interact with the decentralized application. And now you can just download the extension for Chrome for a few megabytes, beautiful!
To make everything clear, let’s take an example of the decentralized exchange Etherdelta, which we recently reviewed. Etherdelta is a decentralized application that runs on a smart ether contract. All exchanges between users occur automatically, without the intervention of a third party. Metamask can be used as a user’s personal account: if you go to the site of the exchange and log into Metamask, you can make all transactions directly from your wallet:
This is pretty much how Metamask will work with an ordinary decentralized application. Just in case, let’s give a list of all decentralized applications with which Metamask works: https://www.stateofthedapps.com/dapps/tagged/metamask