Structure.Gantt is an extension for the Structure app, so in order to use it, you will need to install Structure first.
Structure.Gantt 1.2 requires Structure 4.6 or later and supports Jira 7.2 or later.
You can install both Structure and Structure.Gantt via the Add-On Manager just like any other add-on. No additional configuration is required. As soon as you install Structure.Gantt, you will be able to build your first Gantt chart.