Installation:

1. Go to the SharePoint Store from your SharePoint Online site or Microsoft Appsource.
2. Search for "Virto Gantt Chart" and click "Add" to install the app.

Configuration:

1. Add the Virto Gantt Chart web part to your SharePoint page.
2. Configure the data source by linking your SharePoint lists to the Gantt chart.

Using the Gantt Chart:

1. Adding Tasks: Click on the chart and enter task details.
2. Modifying Tasks: Use drag-and-drop to adjust durations, dependencies, and completion percentages.
3. Customization: Customize the chart's appearance and timescale to fit your project needs.
4. Advanced Features: Manage multiple projects, export charts, and set user permissions.

For more detailed information about product setup and other details, please refer to the Virto Gantt App for SharePoint Online Documentation.