Often customers have content that they gathered outside the Nosto platform that wish to use in a Touchpoint and use the Asset Manager to upload the content into Nosto. Something important to understand is that content shown in any of the UGC Touchpoints (Email, Onsite Widgets, Screen, Ads) needs to be a Tile in Nosto.
If you have added a piece of content directly via the Asset Manager and can't see it when creating an email campaign, onsite widget, or screen it's because you need to create a manual Tile for that piece of content first and only once you do that you will be able to see it in your touchpoints.
Please follow the steps in this article.