Hi Cindy. You can see the answer to your question on page 27 of the user manual. You have to check the manual to understand the answer better as you will see the icons you need to drag to answer the call. If you don't have the manual yet, you can download a copy from the ZTE Quartz page.

when a call comes in, you will see a button appear on the screen... slide the button to the left to not answer, and slide to the right to answer...