You add the string to be split and the delimiter.
You can add these as strings directly like:
'string;to;split'
the delimiter input
';'
Or set the inputs by using variables that you create before running the split activity.
The result will be a list of splititems from the corresponding entity.
If the string is something like ‘ABCD’ then use '’ (2 single quotes) as delimiter to get list of Splititem with A B C and D.
The Java actions return an error if the string to split is empty, so check that or use proper error handling.