An attachment is any file or document that you upload to your page. For example, screenshots, photos, Word documents, PDF files, videos, audio files, or even presentations. Atlassian calls attachments usually “Files” in their documentation.
When there are attachments on a page, you’ll see a small paperclip icon next to the breadcrumb link. Click on the paperclip to go to the attachments dialog, where you can see and edit the entire list of attachments.
The attachment dialog:
Please watch our Video #19 of the Video Tutorial Series “Learn Atlassian Confluence”. Starting with this page of Atlassians documentation you can learn more about attachments as well.