This is a programmer of the module ESP-01 or ESP-01S with converter usb-ttl (its in the image). When Switch Prg is short, ESP-01 is on programmer mode, you must reset the module with Rst switch, this way the usb serial will be recognized.
Besides this PCB is thinked for use with the antena NRF24L01, on the pads P1..P8.
(Coming soon done!).