In the course creation process, and after choosing to manually create your content, you clicked on the "Add Button". Follow these steps:
Click on "Mixed Content"
You can add multiple types of content (text, image, video, audio, PDF, or website)
If you choose text, just write the text you want your learners to learn about
If you choose any type of content other than text, upload the file, or insert its link
Drag the toggle on the right side in the "Settings" to assign to the paragraph an estimated time to read
Click on "Save" to save the text or "Close" to discard the changes