The IRS considers undocumented cash
income (no W-2 or 1099-MISC), for work performed, to be self employment income.
Enter at "Business Income & Expenses" and TurboTax (TT) will
complete Schedule C or C-EZ for you and allow you to deduct any expenses
associated with this income. You'll also have to pay self employment tax
(social security) on any profits greater than $400.
You may have to upgrade to the Self
Employment version of TT. You cannot use the free edition. But you may want to try this first: https://turbotax.intuit.com/taxfreedom