Open the My Digicel App & select Phone Top Up, then select the credit card top up option. You will then be asked if you want to enable top up, select yes and follow the steps.
If you wish to use the website, open www.digicelsamoa.com click on on the 'Sign Up' tab and fill in the details to register. Here's an example of how to create a new account:
Once the account is created, you will receive an email requesting Confirmation of Registration to activate your account.