Adding to existing excel file from datagridview

I'm trying to figure out what would be the easier method for what I'm trying to accomplish. What I have is in, on the main form, a datagridview that is bound to an xls file. I then have another form that the user can import/paste data to another dgv. This content then needs to be appended to the end of the main form's dgv. Would it be easier to add it straight to the dgv and then save it to the excel file or save it to the excel file and reload the dgv? Or does it matter? I'm not exactly sure how to do either method but I figured I would start here.

Ok, so reading up on this it seems it would be easier to add it to the DataTable and reload the DataGridView? That, I'm not exactly sure how to do. I'm not that good with loops or arrays which I'm sure it would require one of those. Anyone have any insight on this?