Note: If you do not have any Service Plans Created in your Reseller Control Panel Please check this guide first: Getting Sarted with Plesk
To create Hosting (Called Subscription in Plesk), you need to add Customer First, to do so:
1. Click on Customers in left Panel.
2. Click on Add new Customer in right Frame.
3. Provide Details of your Customer and fill login details of your customer which can be used by your customer to use to login to plesk and access his domain.
4. Lower part of page will give you option to provide Domain Name & FTP login details for the particular website, so provide Username & Password and make a note of it to access FTP.
5. Choose Porper Service Plan out of the plans you have created under your reseller account, and submit the form and you are done with hosting of Site.
NOTE: We recommend to create different subscription for each domain even if you want to add them under a single customer account, just Go to Customers list page, Click on Particular Customer Name and on next page Click on Add new Subscription and you can add another website under same customr account, so your client can have same Control panel for multiple Websites but different FTP for each site.
if you are moving site from HELM Server to the new Plesk Server, please read this helpful guide at: Moving Website from HELM Server to Plesk