Download &install the Metamask Wallet either from the app store on your phone or the browser extension for desktop.
Head over to bridge.base.org, connect your wallet on the Ethereum blockchain. Choose how much ETH you would like to bridge from the erc20 network to Base. Remember to leave enough for gas fees.
Head over to Sushiswap and paste the $GTR contract Address listed on this website to swap your ETH.
Now all you have to do is add the $GTR contract address to your Metamask Wallet for your $GTR tokens to show. Welcome aboard!