You enter your income based on your own records. You do not need your clients to send you tax forms.
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.