In onchange function first we have to go in .py file (python file)
After that we have to decide where you want to give onchange function and then give attribute on_change to that field.
Like below python code in py file :

 def onchange_function(self, cr, uid,ids,qualification, context=None):
        print"=====qualification======",qualification
        if qualification=='a1':
            a1 = 'Shiva1'
        elif qualification=='a2':
            a2 = 'Shiva2'
        else:
            a3 = 'shiva3' 
        print"=====a1====",a1
        obj = self.pool.get('hr.role1').search(cr ,uid ,[('name','=',a1)])
        print"=====obj====",obj
        a2 = self.pool.get('hr.role1').browse(cr, uid, obj, context)
        for val in a2:
            print"=====a2====",val,val.id

            values = {

                'termination1' : val.id,


            }
        return {'value' : values}