For those who are new OTA is (Over The Air) upgrade works when device is connected to your router what it allows you to do is download and flash without hooking it to your computer! So lets say you have your nodemcu or espbasic dev kit in your project no need to disassemble it or run a cable to it to upgrade you just insert OTA link in settings page save it then click upgrade.
For more info visit the link in my signature on how to do OTA.
Enjoy!
Where I buy my ESP8266 boards from... (Banggood)