Hi, I see many question about using the GrildField & sortable module , so here is an example of how to get the working (tesed on SS3.0.1):
download the files & see the example , I provided a basic template file too so you can give it a quick drive test ;)
Note that you will need to download the Sortable Module from : https://github.com/UndefinedOffset/SortableGridField