To add tokens to MetaMask, open the extension and go to the "Assets" tab. Click "Add Token," then switch to the "Custom Token" tab. Enter the token contract address, which you can find on platforms like Etherscan. MetaMask will auto-fill the token symbol and decimals. Verify the details, click "Next," and then "Add Tokens." The new token will now appear in your wallet. Ensure you're on the correct network for the token you want to add.