When you start ArcCatalog for the first time, the Catalog tree has a branch for each local hard drive. Branches for coordinate systems, database connections, geocoding services, Internet servers, and search results can be added by clicking the Tools menu and clicking Options, then checking the check boxes next to the branches you want to add to the Catalog. You can view the contents of a branch by double-clicking it or by clicking the plus sign beside it.

You can also create new branches in the Catalog tree to make it easier to navigate to your data. These branches are called connections.