voronoi

hello! i have to use Grasshopper for one of my projects and i have a very limited time  + i just downloaded Grasshopper and i really don't have a clue about how it works...so i have decided to use some pre-defined voronoi definitions in my work . i'm in need of  good tutorials and some voronoi definitions for rhino grasshopper .....i'll be glad if anyone can help me to find them :)