The Attachments tab applies to any item which may have an attachment added to it. The following example is for a file upload attachment on a task.
Attachments are added to items using Add icon and selecting the type of item you would like to add as an attachment. The download icon will be available if the attachment can be downloaded. Issues, To-Dos and Approvals may be associated with a task without being located on the task as attachments.
More details on adding files are covered in the Add File and Add Multiple Files topics.