It doesn't matter as much at post #9 as it does at post #109. But I have seen and contemplated acquiring one, but studied them a bit in spite of never getting around to it. Basically, it's an AVR 328 style processor on the same board as an ESP, which is super easy due to the small size of the ESP module. There is usually a pin header to set the serial connections for programming and operating the AVR, the ESP, or both. In the last case, they communicate via serial over the jumper pins as mentioned. Then, different options for sketches come into play. You can have the AVR drive the ESP via AT commands, and perform network operations, or you can program the ESP to take over tasks like networking and data collection, and send that information to the AVR (aka UNO).
So one question I ask is, how have you configured the on board jumpers, if there are any?
Although, from reply #6, it sounds like some rudimentary communication between the PC and Arduino did succeed. So I don't know... a complete compiler error log would help.