If you want to add a file to an already existing topic, go to the Project Overview page and find the topic you want to edit.
At the top right corner of the Topic tile you will see a small triangular icon. Click this icon and select "Edit story" to get to the Topic edit screen.
Alternatively, you can click on the "+" symbol to create a new topic.
On the topic edit screen, scroll all the way down to the "Files" section.
Click on "Upload Files" to select files from your computer. Once the file was uploaded successfully, the name will appear below the button. You can add and remove as many attachments as you like.
To publish the changes, click save. If your program is already live, you will be asked to confirm the change.