For comprehensive documentation on ITS (or just about any other SAP component) go to service.sap.com (using your OSS ID) Search for ‘Install Guides’. Follow this menu path to get to the ITS Install Guide: Installation & Upgrade Guides/SAP Components/SAP Frontend Components (ITS/GUI)/SAP Internet Transaction Server/ – then select your version.
FYI- this technology is old, and frankly klunky. I would recommend using BC, Java Connector, .Net Connector, or SAP Web AS. Go to ‘Connectors’ in service.sap.com to find the solution that best fits your needs.