Hello, Ayodele. 

Ideally, If you want to purchase a one-time license in QuickBooks Desktop, you can continue to use the software as long as you like. However, be aware that support for your product will end three years after its release. To learn more about product policy, you can read through this QuickBooks Desktop service discontinuation policy article.  

Also, when you purchase a license, you'll need to install the QuickBooks desktop either on your computer or mobile phone so that you can input the details of your QuickBooks license number and a product number. 

Additionally, you can reach out to our support team for additional help or other options in using QuickBooks.   

Thank you for posting here in the QuickBooks Community. Don't hesitate to leave a comment below if there's anything else you need. Take care!