Pages has its own file format that is not readable on Windows computers or in Scholar. If you're going to submit your assignment that you've made in Pages, you'll first have to convert it to Word or PDF. This is simple to do.
When you're done writing your assignment, choose Export To from the File menu. Then, choose PDF to export to PDF (this is usually the better option) or Word to export to Word (only if your instructor tells you to).
A menu will pop up with advanced settings. The settings already there are usually fine, so just click Next.
You'll then see your computer's save dialog. Pick a name and click Export.
Your work will be saved as a PDF or Word document. You can upload this document to Scholar or send it to your instructor.