Hi Sam,
If you claim the trading income allowance, box 10.1, you cannot claim any expenses. Boxes 27 - 30, you complete as appropriate.
Class 2 and class 4 National Insurance contributions (NIC) is charged on self employment net profits. They are compulsory when the net profit exceed a certain amount. You camn see guidance here:
Rates and allowances: National Insurance contributions
When the net profit is below the NIC level, class 2 is the only one that can be paid voluntarily and this is done by ticking box 36. You would only need to tick box 37 if your net profit exceeded the class 4 nic level and you were exempt from paying it because you reached State Pension age on or before 6 April 2023, were aged under 16 on 6 April 2023 or were not resident in the UK for tax purposes during the 2023 to 2024 tax year.
Thank you.