To add a domain via Plesk you need to do the following:

1. Log into Plesk

2. Click on "Subscriptions"

3. Click in "Add New Subscription"

4. Fill out the fields:

    Domain name

    Select the IP you'd like it on (Where applicable)

    Username

    Passwords

    Enter a description if you'd like one.

5. Click ok to save the domain/subscription.