Some collections work best when accompanied by extras—this can be anything (pdf, jpg, word document, audio, etc.) that a customer can download and use along with the collection. After Uploading Extras, you can add them to collections so they will appear under Resources on the collections page.
Navigate to the collection you want to add extras to under Content > Collections and click Edit. Under the Extras tab, click Choose File to add an extra. Select the Extra(s) you want to add and then Save.