VB.NET

Imports Microsoft.Office.Tools.Ribbon
Imports Microsoft.Office.Interop.Excel

Public Class Ribbon1

Private Sub Button1_Click(sender As Object, e As RibbonControlEventArgs) Handles Button1.Click

   Dim workbook As Workbook = Globals.ThisAddIn.Application.ActiveWorkbook

   Dim worksheet As Worksheet =  Globals.ThisAddIn.Application.ActiveSheet

   Dim range As Range = Globals.ThisAddIn.Application.Selection

   Dim cell As Range = Globals.ThisAddIn.Application.ActiveCell

End sub

C#

using Microsoft.Office.Tools.Ribbon;
using Microsoft.Office.Interop.Excel;


namespace test
{
    public partial class Ribbon1
    {
        private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            Workbook ActiveBook = Globals.ThisAddIn.Application.ActiveWorkbook;

            Worksheet ActiveSheet = Globals.ThisAddIn.Application.ActiveSheet;

            Range ActiveCell = Globals.ThisAddIn.Application.ActiveCell;

            Range SelectedRange = Globals.ThisAddIn.Application.Selection;