Content Editor is the best way to create optimized content from scratch. Watch the video tutorial or read a full-blown guide.
Karolina prepared a great video tutorial on the Content Editor, this is the best way to learn how to use it.
Do you prefer reading? Tomasz crafted a full-blown guide on using the Content Editor, you can find it here: https://surferseo.com/blog/how-to-use-content-editor/
These are the recommended resources to learn how to use the Content Editor. Enjoy!