Troubleshoot adding files

When I try to add a file to Perforce P4 Server, I get an error stating that the file is not "under client's root." What does this mean?

To add a file to Perforce P4 Server successfully, the file must be saved in your client workspace Directories on your machine where you work on file revisions that are managed by P4 Server.. If you do not know what this means, see your Perforce P4 Server administrator.