Getting value of a particular cell from datagridview on button click

in your row command event handler of the grid view, code something like this

Private Sub GridView1_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles GridView1.RowCommand
 'create a variable to read the content of cell, the primary key of the record
       Dim myprimarykey As Integer
'read the value from the row(which is clicked) and cell (no) 
       myprimarykey=gridView1.Rows(e.CommandArgument).Cells.Item(0).Text
' write the code you want to be performed on it. e.g.
       MessageBox.Show("You pressed the button for the record" & myprimarykey)
end sub

you can also utilize e.CommandName (put the commandname in button description when designing gridview and adding a button column,) perform if-else to check which button was pressed (if the grid offers more than one type of button)

for more help, refer
http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.gridviewcommandeventargs.aspx[^]