How do I transfer ETH from mainnet to Optimism?

Could you please explain the process of transferring ETH from the mainnet to Optimism? I'm a bit unfamiliar with the technicalities and would appreciate a step-by-step guide. Is there a specific wallet or platform that I should use for this transfer? Also, are there any fees involved, and how long does the transfer usually take? Would it be different if I were to transfer another cryptocurrency instead of ETH? Thank you for your assistance.