ESP8266 DevBoard

Various NodeMCU and related development boards.

These are connected directly to your USB port with a USB micro cable.

They typically reboot whenever your PC opens the serial USB connection. Open the flasher and then start the flashing operation (on the correct comm port!). The flasher app should put the device into flash mode automatically when flashing starts (be sure no other application is connected to the usb/serial port). Reset or power cycle when complete.