We carry a few different ESP8266 boards so I'll need you to specify which one you are trying to use. It may be that you are using the ESP8266 Thing (https://www.sparkfun.com/products/13231) and if that is the case, the USB connector is only for power/charging a battery. To program the board, you need to use a USB to serial bridge like an FTDI or something similar. We cover this in more detail in this section of our Hookup Guide: https://learn.sparkfun.com/tutorials/es ... -the-thing
If you are using a different ESP8266 board that has a USB to serial bridge like the Thing Dev (https://www.sparkfun.com/products/13711), let us know and we can troubleshoot further.