By default, Cucumber for Jira is not activated in your Jira project, so you should first activate it in the project settings.
Activate Cucumber for Jira on your Jira project
Just after installing Cucumber for Jira on your Jira Cloud instance, go to your Jira project in Project settings. Select Cucumber for Jira, and activate Enable Cucumber for Jira.
As soon as Cucumber for Jira is enabled, a new menu entry, Living Documentation, appears on the left side of the Jira project page:
And the Cucumber panel can be displayed in a feature issue.
You can now create your first living documentation.