Espressif Systems ESP8266 Beginner's Manual page 36

Next, change the interval on line 59 from 1000 to 500 milliseconds, and click upload. You should get a password prompt: enter
"esp8266". This password is set on line 31, so you can change it if you want to. You can also delete line 31 altogether to use it without
a password, but it's not recommended - for obvious security reasons.
The sketch should upload just fine, and once the ESP has reset itself, the LED should blink twice as fast.
Once in a while, you might get an error saying . If this happens, just enter the password, and try again.
[ERROR]: No Answer
Serial Monitor OTA
Using the Serial Monitor over Wi-Fi is not possible (yet?). When you try to open it, you'll be prompted a password, entering the
password won't work, because there is no SSH support to access the ESP's console.
You can use a different program to get debug output from the physical Serial port. On Windows, you can try Portmon. On Linux, you
can try GTKTerm ( ) or Screen ( to install, and or
sudo apt-get install gtkterm sudo apt-get install screen screen /dev/ttyUSB0 115200 screen
to run; to exit).
/dev/ttyACM0 115200 CTRL+A, CTRL+D