Here are all the webinars given by David Rutten, the creator of Grasshopper:
Introduction to Grasshopper with David Rutten:
David Rutten’s Introduction to Grasshopper Webinar:
Advanced Topics in Grasshopper:
You can also access Rhino tutorials on their Vimeo Channel (https://vimeo.com/rhino). You will see amazing tutorials such as an intro to the Scan & Solve structural analysis (Michael Clarke wrote a post on it previously: https://wewanttolearn.wordpress.com/2012/11/08/scan-and-solve-for-rhino/):
Welcome to Freeform Modeling In Rhino