A self assessment tax return comprises of the main tax return (SA100) and several supplementary pages Self Assessment tax return forms
You would need to complete SA102 for employment and SA103 for self employment. You can use SA103S, if your turnover is less than £85000.00.
It's possible that you are confusing VAT and expenses. VAT is separate tax to income tax and is not covered in this forum, nor shown in a self assessment tax returns.
As self employed, you have to claim vehicle expenses for the proportion of the mileage used, wholly and exclusively in the performance of your self employment duties, you can find guidance here-
Expenses if you're self-employed
You may wish to contact the VAT helpline here
VAT: general enquiries