Assets are things that you upload or create in Pebble+.  You can upload any type of digital file using the Upload New panel on the homepage, from the Burger menu, in the asset store, or even while working on another asset, like a portfolio.  All uploaded files are Assets and can be found in your Asset Store.  You can also create things in Pebble+ via get Creative (on the homepage or in the burger menu)  or by using templates or workbooks from the Resource Store.  When you Save any of these items they become Assets in your Asset Store.  Assets contain personal content - content that you have added, that is meaningful to you, and that you can go back and edit or delete as required.