Plain text is like writing with a regular pencil on a blank piece of paper. When you do that, you can only use simple letters and numbers, and you can't add any fancy colors or pictures to your writing. That's basically what plain text is. It's just simple words and numbers without any special decorations or formatting.
Plain text is easy to read by both humans and computers, and it's also very easy to transfer from one computer to another because it doesn't have any complicated stuff in it. You can write plain text using programs like Notepad on Windows or TextEdit on Mac, and you can save it as a file with an extension of ".txt".
Some people like using plain text because it keeps things simple and makes their writing look more professional. Plus, it's less likely to have any errors or compatibility issues when sharing it with others.