To use Sonne Finance, you need a MetaMask or web3 wallet connected to the Optimism Mainnet. For more information, visit their website.
Metamask by default only supports the Ethereum network. However when you connect MetaMask to Sonne , Sonne will automatically configure MetaMask to work with Optimism Mainnet.
To perform transactions on Sonne or any other Optimism protocols, you will need ETH for gas. You can see the current bridges to optimism here: https://www.optimism.io/apps/bridges
Or you can watch this video to learn how to bridge ETH or other tokens to Optimism Mainnet: