Once you've completed the Rent To Own program for Serum, Splice will email you a copy of the serial number to the email associated with your Splice account. Open Serum in your DAW and it will prompt you to enter that serial number. You no longer need to have the Splice application running or a internet connection to use Serum.
To activate your Xfer Records account go to https://www.xferrecords.com/users/password/new
Enter the email address associated with your Splice account and Xfer Records will send you a "Reset Password" email to that address. Choose a password and then you can login to Xfer Records.