I registered a small business in 2024. I have startup costs and expenses. I have not received income for this business yet. Where do I enter "0" for self-employed income?

If you are a single member LLC, and you did not have any income in 2024 as you were not yet operational and open for business, you do not need to file a return for the business.

In 2025, if you are operational and have income, then you would include any expenses you had as start up costs on your return for 2025.