When you fill out schedule C in your personal return the program will ask if you use the Cash Method or Accrual Method to report your income and expenses. The most common method is CASH. It means you report your income in the year you actually receive it and report your expenses in the year you actually pay them. See,
https://ttlc.intuit.com/community/business/help/what-is-the-cash-method-of-accounting/00/25658
It will also ask if you are "at risk". If you have money not at risk you can not take a loss on schedule C. If you don't know what it means then probably All your Investment is at Risk. It means you are using your own money for the business.
Money is not "at risk" for the following:
---Non-recourse loans used to finance the business
---Cash, property or borrowed amounts used in the business that are protected against loss by a guarantee, stop-loss agreement, or other similar arrangement (excluding casualty insurance and insurance against tort liability).
---Amounts borrowed for use in the business from a person who has an interest in the business, other than as a creditor.
