Since we will be using the Goerli testnet you'll have to switch from "Main Ethereum Network" to "Goerli Test Network" in your MetaMask by selecting it from the top right dropdown.
After switching to the Goerli testnet you can go ahead and acquire some Goerli testnet ETH by following these steps:
Copy your address. It is located on the left hand side in MetaMask and starts with "0x".
Visit the Goerli faucet, there you'll have to paste the address into the input field and check the "I'm not a robot" checkbox.
Click on "REQUEST 0.05 GÖETH".
You will see a success message when the request has gone through. If it fails, keep trying until it succeeds.
You can verify that 0.05 GÖETH was actually received by opening MetaMask and see if your Goerli Test Network shows a balance of total 0.05 GÖETH.