If you are a non-resident landlord, you are required to complete the SA100 (Main tax return), SA105 (Property schedule) and SA109 (Residency schedule).
Looking at each one and relating it to its use on GoSimpleTax:
SA100 (Main Tax Return)
This form will include your own personal details. This will be completed when you complete the 'Personal details' page. Your name, UTR, address, date of birth and NI Number will be entered on this page.
Don't worry if the PDF preview isn't showing your address before you send, this is sent in the background but doesn't show on the PDF download as it is an electronic viewing.
SA105 (Property schedule)
On this form you will add in your 'Rental income' within the 'Income' section of the page. If you have had tax deducted from your rental income, you should include this on your rental income entry, there is a box relevant to this there.
In the expense section, you should include all your expenses incurred for the purpose of running the rental business; insurance, ground rent, any bills paid for on behalf of the tenants, agent fees, management fees, repairs and maintenance etc. However, if your expenses are less than £1,000, do not include your actual expenses, instead use the property allowance - this should be entered in the 'Income' section of the property page.
For more information, see HMRC guidance on this:
SA109 (Residency schedule)
You should press the EDIT button after adding the page to answer the questions relevant to this schedule.
On this form you will declare your non-residence, stating whether you have visited the UK and how long for during the tax year on the first tab. On the second tab, you would include whether or not you are entitled to a personal allowance in box 15 or/and 16. If you are unsure, visit the HMRC help notes:
Instructions can be found below on how to add your personal allowance if you're entitled to it:
You should also state in Box 17 where you are currently resident and where you are considered a national.
The other boxes on this schedule may be relevant, so make sure you refer to the help notes link above to see if you are required to answer any other boxes. Usually domicile and remittance basis isn't relevant for non-resident landlords, so it is unlikely entries are required for Boxes 23 onwards, however, ensure you seek advice where you think they may be required.