How to store the information we type on the grid in the form

We are developing an application which requires us to store or save the values we input in the grid to a File and also on opening that file we are supposed to get the values in the grid. Can Anybody let us know how to develop such an application using DHTMXTreegrid

dhtmlXTreeGrid supports serialization to XML, you can call
    var text=treegrid.serialize();

to receive all data of treeGrid as XML string, after that you can send data to server ( by hidden form, or post ajax call ) where it can be stored as file.
The format of serialization is the same as format used for loadXML, so you can use such file as source of treeGrid.