The File/Import/Case... ribbon tab item is used to read in a Fluent case file (extension .cas.h5), or a mesh file (extension .msh.h5, .msh, .grd, .MSH.h5, .MSH, or .GRD) that has been saved in the native format for Fluent. See the  User's Guide for details.

The File/Import/Case... ribbon tab item opens the Select File dialog box which allows you to select the appropriate file to be read. For more information see Importing Fluent Files in Workbench.