Help on US 2021 Federal + State tax returns

I'm a bit confused on self employment / solo proprietorship taxes and how the standard deduction applies. I have all the numbers needed and generally know what to do but I need guidance. It might be easier to fill out yourself. I also need help regarding a letter from the IRS about my 2020 tax return. They said I may be liable for additional self employment tax, but it wasn't clear if I actually owe more or not or what to do.