Tools in XNAT marketplace are external scripts and applications that do not integrate directly with a core XNAT installation. They typically will interact with an XNAT via XNAT's extensive REST interface. Much like Add-Ons, Tools are diverse so it is impossible to provide much direction on how to use a general tool. For that reason we encourage developers to provide adequate documentation and either attach or link to it on the Tool's details page. If you are having trouble, feel free to ask for help on the xnat_discussion Google Group.