Next to Alias Name, type in the subdomain you set in LaunchRock.
If you chose signup.mydomain.com then put: signup
Next to Points to Host Name, type in host.launchrock.com
Congratulations! Your CNAME record is now configured to point to LaunchRock.
If you have trouble configuring your CNAME records, you can check out the Wix tutorial page. Or, view a sample message to use when you contact Wix.com for assistance.
Once you've modified your A records, it may take up to 72 hours for changes to update live.