How do I add Harmony One to MetaMask?

Could you possibly explain to me, in detail, the steps involved in adding Harmony One to MetaMask? I'm a bit new to this and am finding it a bit challenging to navigate through the process. Would it be necessary to download any additional software or extensions? Also, are there any specific settings or configurations that I need to adjust in MetaMask prior to adding Harmony One? Additionally, could you clarify any potential security measures I should be aware of when performing this operation? Thank you for your assistance, I appreciate your help in guiding me through this process.