You may receive income from several different types of sources during a tax year.
The payers of that income typically send you a form listing how much they paid you and the amount of taxes withheld. Forms you may receive include Forms W-2, 1098, and 1099. This includes any form with a 1098 or 1099 prefix, such as the 1098-E, 1099-B, 1099-MISC, etc.
In TaxAct, you will need to enter these amounts when prompted. The amounts will then flow to the necessary line and form.