You can handle the grid.RowEnter event.
private void gridDataBoundGrid1_RowEnter(object sender, Syncfusion.Windows.Forms.Grid.GridRowEventArgs e)
{
//put the value in column 1 into the textbox
string s = this.gridDataBoundGrid1[e.RowIndex, 1].Text;
this.textBox1.Text = s;
}