Learning Grasshopper (or GH in short) can be an endless google quest, especially in the beginning. The software and its documentation has gradually been developed and is for the most part based on an open source community.
StudioFG can help integrate Grasshopper into an office workflow and offer customized workshops, but there are some good starting points here to make a start for yourself:
- One of the most important sources is this forum, hosted by the creators of GH themselves: https://www.grasshopper3d.com/forum/.
- TOIpedia of TU Delft also offers some good starting points: http://wiki.bk.tudelft.nl/toi-pedia/Grasshopper.
- And of course good old Youtube: https://www.youtube.com/results?search_query=grasshopper+3d+tutorial