In Gmail, use the Reply all button to send your response to the original sender and everyone listed in the "To" and "Cc" lines. This option appears below the email message on both desktop and mobile app versions, ensuring all participants in the conversation receive the reply. 

You can flag (or star) an email if you want to remember it is important, and this also puts it in a folder (or a specialized view/label). Flagging serves as a visual reminder and acts as a tool to organize important messages for later, often aggregating them into a dedicated folder or list. 

Unfinished emails that are composed but not sent are stored in the Drafts folder. This folder acts as a temporary holding area, allowing users to save their progress, edit, and send the message later. 

The From field indicates the sender's email address. When you compose a message, this field is usually automatically populated by your email client with your own address to identify you as the source of the email. Standard email protocols (such as RFC 5322) require this field to be present in the email header.