Hello,

on the button call the method. and into the method write your code to generate the excel report.

here i am write some code from where you can get some basic idea.

import xlwt
from xlsxwriter.workbook import Workbook
from cStringIO import StringIO
import base64
class your_object(models.Model):
    _name = 'your.object.'
    @api.multi
    def generate_excel_report(self):
        filename= 'filename.xls'
        workbook= xlwt.Workbook(encoding="UTF-8")
        worksheet= workbook.add_sheet('Sheet 1')
        style = xlwt.easyxf('font: bold True, name Arial;)
        worksheet.write_merge(0,1,0,3,'your data that you want to show into excelsheet',style)
        fp = StringIO()
        workbook.save(fp)
        record_id = self.env['wizard.excel.report'].create({'excel_file': base64.encodestring(fp.getvalue()),
                                                                                                'file_name': filename},)
        fp.close()
        return {'view_mode': 'form',
                    'res_id': record_id,
                    'res_model': 'wizard.excel.report',
                    'view_type': 'form',
                    'type': 'ir.actions.act_window',
                    'context': context,
                  'target': 'new',
       }

class wizard_excel_report(models.Model):
    _name= "wizard.excel.report"
    excel_file = fields.Binary('excel file')
    file_name = fields.Char('Excel File', size=64)

make the form view(xml code) of "wizard_excel_report" object as per your needs