Ah, if I had known you were fine with the ESP8266, then you have tons of options. My personal favorite is this sonoff:https://www.amazon.com/Sonoff-S31-SONOFF-Plug-White/dp/B08TNF4835?&linkCode=ll1&tag=ana024-20&linkId=91dd8939463e4f8b9685b32e7f79b3ba&language=en_US&ref_=as_li_ss_tlI usually just flash them with Tasmota, but they have pads that are labeled inside for flashing (you still need the TTL flasher). Plus they're cheap and do power monitoring. :)

For the one you got, if you can't find specific instructions, then here's the main things - normally I like to hook up the RX/TX/GND first, then you should be able to see the ESP printing things if you just run a terminal on your computer. Once you know you have that working, then you need to identify GPIO0, you need to pull it low when booting - it should print something about it being ready to download firmware, then just exit the terminal and flash with whatever method you want. For things like Tasmota, they now even have a web-based flasher that works really well.