How do I insert a copyright symbol?

Could you please elaborate on the steps involved in inserting a copyright symbol into a document or online content? I'm particularly interested in knowing if there's a universal method that works across different platforms, such as word processors, web browsers, and social media. Also, is there a specific keyboard shortcut or special character code I should be aware of? It would be great to have a concise yet comprehensive explanation of this process, as I often find myself needing to include copyright notices in my work. Thank you for your assistance in this matter.