If you have a NT code by way of DTA, you would need to complete the form HS302 or HS304 depending on your circumstance and attach that to your tax return on the SA109 page.
If you read the instructions for either of the helpsheets, it will tell you to deduct the amounts included on the form from box 1 and 2 on the SA102 page.
If all your income is not taxable in the UK (meaning you haven't worked in the UK during the tax year and you have no duties here) then you would have an employment page with no income or tax included because of the claim on the SA109 schedule.