Everyone on Slides has access to their own media library but if you're part of a team you also have access to a second set of shared media. This shared media accessible to everyone in your team but can only be edited by team administrators. It's a great way to avoid each team member having to individually locate and upload the assets they need.
Team media is can be accessed through a tab in the header of the library. Find out more about the media library features at http://help.slides.com/knowledgebase/articles/552825-media-library