Markdown aims to be a markup language that's natural to write and read, as if it were typed on a typewriter. You can write in Notepad, or whatever text editor you prefer, and copy/paste it into an e-mail, or save it as a .txt file and send it to us as an attachment if you like. **StackEdit isn't a necessary part of the process**; it just helps you see what the conversion to HTML will look like. It also gives you buttons for all the features.
For the most part, you just write as you normally would -- paragraphs are just blocks of text separated by two carriage returns, and the Markdown parser will turn them into HTML paragraph tags for you.
You can emphasize a bit of your text by wrapping it with asterisks: *one asterisk for emphasis (italic)*, and **two asterisks for heavy emphasis (bold)**. If you prefer, you can use _single_ or __double underlines__ instead of asterisks.