Hi Ranjith,
By now, you must be able to make Db calls for add/insert/update/delete a records in the DB.
So, im not going to tell you how to do that.
For, getting the GridView Footer row's Textbox value, you can search it this way,
((TextBox)GridView.FooterRow.FindControl("Textbox_Name")).Text;
This should get you the value. You can get the rest of them similarly and make a Db call to save the values.
Happy Coding.!
Thank you,
Vamsi