Note that if you are not sure which esp8266 you model you have, check it out here.
Before we flash, lets do some simple wiring :
-wire 3v3 and ground.
-wire tx to rx, and rx to tx (I use a usb to serial ftdi adapter)
-set gpio0 to low (ground)
-set ch_pd (also referred to en) to high (3v3)
-power off/on to enter flash mode
It is as simple as put your firmware next to flashesp8266.exe (in my case firmware is ESPEasy_mega-20180102_normal_ESP8266_1024.bin) and execute ESPEasy Flasher.
Once flash is completed, set gpio0 free (but leave ch_pd high), power off/on and you should see a new ssid on your network called esp_easy_0 (password=configesp).
configure it i.e connect it to your wireless network and you are done.