Getting Started With the ESP8266 ESP-12 : 8 Steps ...
The ESP-12 has a 2mm pitch, which means you cannot access all the pins on a breadboard or a perforated / dot matrix directly, which have a 2.54mm pitch (distance between adjacent pins).. You could use a Xbee adapter board, but there's an easier way out. Take a small length of single strand cable or multi strand cable, and get a spider web breakout like this.