At first, the Catalog application should be added to your Jira. Read how to find, add and manage the Cloud apps (Atlassian documentation).
You can trial Catalog free for 30 days. Once the trial period is over, the cost of the app will be automatically included in your next bill for monthly cloud users, unless manually deactivated. Check the Atlassian FAQ dedicated to marketplace apps for more information.
What will happen with data if my license is stopped?
The Catalog section and settings will not be available. However, the custom fields will stay and you will be able to keep using them as regular select lists. All the Catalog data will stay safe in case you want to proceed with the app.