As well as importing employees from a CSV you can also import employers from a CSV file rather than manually create them.
Go to the Employer Dashboard and click the Import button.
You'll find a link there to download your existing employers to a CSV file so that you know which column headings to use when you build your import file.
Upload your file and you'll be shown a preview of the data.
IF you're happy with what you see then click the button to import the employers
Any Employer Defaults you've set will be applied and the employers will be created.
Once the employer records have been imported you can then import employees via one of the many methods available (CSV, FPS, etc)