After clicking on the Buy button, Ubuntu Software Center will prompt
you to login or create an Ubuntu Single Sign On account.
Ubuntu Single Sign On (Ubuntu SSO) is a service provided by Canonical
Ltd that allows users to login to multiple websites and access
multiple services. Use your Ubuntu SSO to login to the following
- Ubuntu One
- Ubuntu Shop
If you already have an Ubuntu Single Sign On account, proceed with
your software purchase:
- In the More Info screen, click on Buy
- Login to your Ubuntu Single Sign On account
- Review the Quantity, Description and Amount of your software
- Enter your Billing address
- Enter your Billing information
- Click Review Payment to proceed (or cancel to stop)
- Review your payment information
- Click Submit Payment to purchase software1
1Source:Ubuntu Software Center Documentation
If the App is free, but shows the buy button and $0.00 like the app in the image below, after you login, you will get
And below is the final outcome. The App was installed without paying a dime.
For repositories, and how they integrate with USC seeIntegration with Ubuntu Software Center.