The graph paramaters are one which are added to the respective graph. You can added the graph parameters by selecting the edit>parameters from the menu tab. Here's the example for the graph parameters.
If you want to run a same graph for n number of files in a directory, You can assign a graph parameter to the input file name and you can supply the paramter value from the script before invoking the graph.
If you have any concerns or doubts pls write back to me.
The Parameters that are private to a graph are called Graph Parameters. They can't be used for all the graphs present in the Sandbox ie. they are limited to the graph for which they have been defined. You can add the graph parameters by selecting the edit>parameters from the menu tab. Graph level parameters can be further classified as -Local Parameters -Formal Parameters