Allow to upload code both to Serial enabled boards (that have an exposed COM port), or devices in other modes (not Com port visible.
to upload to visible device, select it's COM port from the drop down list. and click upload. for a Non visible device, select the proper option and click upload. then reset the device to Bootloader mode (usually "double click" on the devices Reset button.
the program will identify device's bootloader and will upload the selected HEX file.