InstantRig is a dynamic panel. Different rollouts and buttons will be enabled or disabled depending on which part of the rig is selected in viewport. 
Start pressing “Create Root Node” button. It creates the main root controller of rig. When the root controller is selected, the “Hub” button will be enabled in “Create Module” tab. continue creating first hub bone. If the hub bone is selected, different module buttons will be enabled in “Create Module” tab. Then you can continue creating different modules top of hierarchy.

The script can be launched from the button InstantRig available under Exchange Store Menu. See below screenshot of Exchange Store Menu. If you are unable to find the menu, then please reset the workspace and restart the product.

The installer that ran when you downloaded this plug-in from Autodesk App Store has already installed the plug-in. You may need to restart Autodesk® Product to activate the plug-in. To uninstall this plug-in, click Control Panel > Programs > Programs and Features (Windows 7/8/8.1/10) or Control Panel > Add or Remove Programs, and uninstall as you would any other application from your system.