Follow this tutorial if you want to create more than one code.
Through out the creation process, you can click the Save and Continue Edit button in the top-right corner.
1. First, you will need to generate codes using a code generator. Here are a couple of reliable Web sites:
http://generaterandomcodes.com/free-generate-random-codes-tool
http://www.randomcodegenerator.com/
2. Save the file as a CSV.
3. Go to Promotions à Shopping Cart Price Rules.
4. Click on the Import Rules button on the top-right corner.
6. For
the rest of the settings, follow the same (above) instructions for uploading an
Individual Code.
7. Click on the Import Data button once finished.
8. You will be re-directed to a summary of voucher uploads:
9. Wait
a few minutes until “Pending” 
becomes “Done” 
.
10. Once
it is uploaded, you will get an e-mail that indicates it has been successfully
uploaded:
11. Press the Save Rule button 
.