For most of your text based projects you are required to submit a document in PDF format either via Syllabus or My Files tab.
You can easily export PDF from the softwares or applications you are using for writing such as Google Docs, Microsoft Word, Celtx, etc. Please navigate to FILE > Download/Export > PDF. Here are some of the examples:
NOTE: If you need to export your production book from google sheets, follow the similar steps above but make sure you select "workbook" to have all your sheets in a single PDF document.
You can upload PDF documents to My Files Tab or submit as your assignment.
Check this article for more info on My Files & How to submit your assignments