To bridge your existing funds there are several bridges to move between different blockchains. Optimism has a official bridge called Optimism Gateway.
Follow these steps to bridge your Crypto Francs (XCHF) or Ether (ETH).
That's it! It will take up to 20 minutes until the funds will be visible in your wallet. Alternatively for Ether you can use a fast bridge like Hop.exchange in similar fashion. A guide for Hop can be found here.
If you have Ether already or want to buy Ether on a central exchange and then want to move it to Optimism the steps are different for different exchangesAlternatively the bridge wallet of Mt Pelerin allows you to buy smaller amounts via credit card and bank transfer and send them directly to your address on Optimism.