Prince,

Here you go!

#class file yourfile.py

#Example With APi.

from openerp import models, fields, api,

class sale_order(models.Model)

    _inherit = 'sale.order'

    your_field = fields.Char("Your Field Label")

    #instead Char you apply any type of field whatever you need from this field list you can use

    #Char,Integer,Date,Float,Many2one,One2many,Many2many,Related etc...

    #First later of each field type must be capital in odoo  v8. if you follow the v8 codding standard,

#Example Without Api (With v7 codding standard)

from openerp.osv import osv, fields

class sale_order(osv.Model)

    _inherit = 'sale.order'

    _columns = {

    'your_field':fields.char("Label of your Field", size=64),

}

#Now in xml file you can add this field by using xpath concept by inherting exsisting view.

Let me know if you face any difficuties on this.

Regards,

Anil.