Every user of GrafX2 should get "DB's TOOLBOX"[0] - free additional Lua-scripts for GrafX2, that has many samples on API usage.
Latest version is "DB's TOOLBOX v1.4"[1] (released on December 2017).
[0] http://pixeljoint.com/forum/forum_posts.asp?TID=12854
[1] http://pixeljoint.com/forum/forum_posts.asp?TID=26080