Görli Testnet is a testing ethereum netwrok run by Ethereum Foundation for testing the smart-contracts being developed for free.
Goerli uses fake GoerliETH (fake ETH) for transactions.
To obtain GoerliETH it's necessary to ask the network for some using faucets.
MetaMask has to be set to Goerli Test Network first (testing networks are not visible by default).
Faucets I've used before: