The Map Viewer can be a stand-alone map viewing tool. However, the Map Viewer cannot be deployed without an associated GIS Portal Toolkit web application and catalog. When searching for data from the Map Viewer, it can be configured to interact with the Portal or with any other CSW Catalog. From the Portal side, default functionality looks to the Map Viewer when adding data dynamically using the "Add to Map" link for live services. Customizations can be made however to launch in a different viewer application if needed.
Metadata is the fuel that really drives the GIS portal and the whole concept. If you don't already have a mechanism where you are maintaining a metadata about your data, holdings, or your Web site for your documents, then there's an online form in the Portal where you can enter in the metadata individually for each data record you want to document. But, if you're a clearinghouse or if you have lots of content, you're probably already creating metadata about your services, so in that case you have serveral options for publishing content:
File upload from the Portal interface
Exposing your metadata through an ESRI Metadata Service, Z39.50 catalog, Web-accessible folder, or CSW catalog so that it can be harvested.
Use the publishing client from ArcCatalog. can upload your metadata through like a Web-accessible folder, or you can elect to have your metadata harvested again through Web-accessible folders or through the Z3950 connector or a catalog services for the Web connector.