The ESP8266 is a very cheap wifi-to-serial solution for adding Wifi to electronics projects.
Once its been hooked up the fun starts. A terminal emulator like Putty or Tera Term is needed to send commands to the module. To interact with the module it needs to receive AT command via its serial pins.
The simplest command to test it with, well you have guessed it!! “AT” Sending it “AT” (and courage return/line feed at the end to send the command) should return an “OK” result. If not it indicates that the wiring is wrong or if it returns squiggle characters that the baud rate being selected is incorrect.
Don’t forget that courage return/line feed. Putty will send the courage return on pressing enter but a Ctrl+J is needed to send the line feed character.