You can create an UltraViolet™ account either through this website or directly on the UltraViolet™ website.

Via the Universal website: 
Redeem an UltraViolet™-enabled title by following the instructions found in the package insert and the redemption screen prompts.

If your Universal account is not yet linked to an UltraViolet™ account, you will be prompted to create and link an UltraViolet™ account to your Universal account. Once this is done, you can complete the movie redemption process.

Via the UltraViolet™ website:
Go to www.myUV.com and click "Sign Up" and follow the prompts.