The resource type section of the library can be accessed by clicking on the "open" dropdown at the upper left of the screen.
This section contains all the resource types you have access to, and can be filtered using the search bar at the upper right corner of the screen.
Resource types can be created in this section of the library and accessed in all other parts of Riffyn. The method to create new resource types in the library is identical to the way they are created in design mode. More information on creating resource types.