You can browse by resource to see a list of assemblies, procedure libraries, or paths as top-level nodes. When you expand the nodes, the ABL packages or .NET namespaces appear as second-level nodes. Expand these second-level nodes to see the third level of contents -- the types (the classes and/or interfaces).
You are not required to have an OpenEdge project available to browse by resource, which can be helpful if you are browsing external resources.