Can someone give me a little bit of advice on DataTables.

I need to understand how I can manipulate data from within a datagrid bound to a dataset.

To do this do I have to create a datatable or is one created automatically. I am a bit lost on the use of the datagrid and need to get my head around it.

In particular I need to be able to loop through a gris to make appropriate changes.comparisons and am a bit lost.

Thanks in advance