Trigger.old example in Salesforce?

Sample Trigger:

trigger userNamEmaiil on User (before insert, before update)
{
    if(trigger.isInsert)
    {
        for(User u : trigger.new)
        {
            if(u.name != u.Email)
            {
                u.addError('Username and Email should be same');
            }          
        }
    }
    else if(trigger.isUpdate)
    {   
        for(User o : trigger.old)
        {
            for(User n : trigger.new)
            {
                if(o.email != n.Email)
                {
                    n.addError('Email address cannot be changed');
                }  
            }
        }
    }
}

Output: