Go to the sidebar page, click on EDIT (the pencil again) and ADD the link to your topic from the start page by using the Internal Link button on top of the edit window. Save and see …
At any time you can also UPLOAD any type of document, like PDF, TXT …, as also Pictures or whatever you need.
Therefor use the Media Manager (under Site Tools). Now you can link your upload to your page.
Have fun