OpenSprinkler does not have a built-in USB-serial converter so the standard serial monitor will not work.

OpenSprinkler 1.x and 2.0 have a built-in USBtinyISP programmer. When plugging in the USB cable, it will present itself as a USBtinyISP device.
OpenSprinkler 2.1 has a USBasp bootloader and will present itself as a USBasp device in bootloading mode.

To upload a program, you need to first open a program in Arduino. Your screenshots show that you haven’t opened any program (I can only see two # symbols). For further instructions, please check the ‘Upload and Modify Source Code’ section in the Firmware Update instructions. Here is the direct link: