create a field in the database

'state': fields.selection([

('draft', 'Draft'),

('verify', 'Verified'),

('cancel', 'Cancelled'),

('done', 'Approved')],

'Status',  readonly=True,),

copy the code in view file

<header>

<button string="Verify" name="action_verify" states="draft,cancel" type="object" class="oe_highlight" />

<button string="Cancel" name="action_cancel" states="draft,verify" type="object" class="oe_highlight" />

<button string="Approve" name="action_approve" states="verify" type="object" class="oe_highlight" />

<field name="state" widget="statusbar" statusbar_visible="draft,verify,done,cancel" class="oe_highlight" type="workflow"/>

</header>

write the functions in .py file

def action_verify(self,cr, uid, ids, context=None):

      if context is None:

          context = {}

      self.write(cr, uid, ids, {'state': 'verify'}, context=context)

      return True

def action_cancel(self,cr, uid, ids, context=None):

      if context is None:

          context = {}

      self.write(cr, uid, ids, {'state': 'cancel'}, context=context)

      return True

def action_approve(self,cr, uid, ids, context=None):

      if context is None:

          context = {}

      self.write(cr, uid, ids, {'state': 'done'}, context=context)

      return True