Hello,
when you are a beginner, the best seems to begin by tutorials
Read that
and I advise you to begin with Modelab Grasshopper Primer,
https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwiz4rif-urdAhXCxIUKHRgrDskQFjABegQICBAC&url=https%3A%2F%2Faae280.files.wordpress.com%2F2014%2F10%2Fmode-lab-grasshopper-primer-third-edition.pdf&usg=AOvVaw1rpFh1iW-qkIu4S24gbLGL
https://www.modelab.is/grasshopper-primer/
And also read that if you have further question