This tutorial is all about how to control electronic devices using WiFi technology. You have heard the name of NodeMCU ESp8266 WiFi development Board. A lot of guys wrote introductions and tons of tutorials are present here on Instructables. So, Im going to focus on

NodeMCU Setup to upload Code using Arduino.ide
Connecting to WiFi network and getting IP Address
Controlling light using Android App over internet.

Let's proceed.

Step 1: Parts:

NodeMCU ESp8266 WiFi Dev. Board
Micro usb cable to upload Code
330r resistor
Android App

Buy electronic components at utsource.net

IOT_light_ashrafminhaj (2).apk
Download

Step 2: Pinout

NodeMCU's pin out and written 'D' pins are different. Make sure to check them before you hook up anything.

We will connect an Led using with positive end on D4 and Gnd to Gnd of NodeMCU.

Step 3: Setting Up Arduino.Ide

To Upload code to NodeMCU using Arduino.ide

Update Arduino.ide (desktop app)start Arduino appgoto Files > Preferences Then paste the link then press ok. http://arduino.esp8266.com/stable/package_esp8266...
goto Tools>Boards> Board Manager then wait untill it finds ESP8266 properties
Scroll down and click install
Then Restart the Arduino App.

Now you can upload Code in C / C++ to NodeMCU ESP8266 using Arduino.ide

Step 4: Code:

To check IP Address (Internet Protocol) upload the code and open Serial Monitor.

/* Node MCU ESP8266 IOT wifi dev. Board wifi connectivity test   code by Ashraf Minhaj. 
Tutorial on blog  www.youtube.com/c/fusebatti 
for any quory mail at ashraf_minhaj@yahoo.com  
Consider subscribing my youTube channel  www.youtube.com/c/fusebatti    */    
#include    //declare ESP8266 library
const char* ssid="Your wifi name";   //Put your wifi network name here
const char* password = "Password";   //Put your wifi password here
void setup() {
  Serial.begin(115200);      //initial Serial communication for serial monitor  Note:115200 depends on your board  
Serial.println(); 
 Serial.print("Wifi connecting to "); 
 Serial.println( ssid );
  WiFi.begin(ssid,password);  
  Serial.println();  Serial.print("Connecting");
  while( WiFi.status() != WL_CONNECTED )  //while loop runs repeatedly unless condition is false  {                                       //it'll keep trying unless wifi is connected      delay(500);      Serial.print(".");          }
  Serial.println();
  Serial.println("Wifi Connected Success!");  
Serial.print("NodeMCU IP Address : ");   //Shows the IP (Internet Protocol) number of your NodeMcu 
 Serial.println(WiFi.localIP() );         //Gets the IP address of your Board  }
void loop()              //In our case we don't need this but still it needs to be there.
{  // put your main code here, to run repeatedly:
}

Now to Control our project light upload this Code....

The code is also avilable on arduino.examples. I've managed to build an app to make it work with it.

#include 
const char* ssid = "Wifi name";
const char* password = PassWordl";
// Create an instance of the server
// specify the port to listen on as an argument
WiFiServer server(80);
void setup() {
  Serial.begin(115200);
  delay(10);
  // prepare GPIO2
  pinMode(2, OUTPUT);
  digitalWrite(2, 0);
  // Connect to WiFi network
  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");
  // Start the server
  server.begin();
  Serial.println("Server started");
  // Print the IP address
  Serial.println(WiFi.localIP());
}
void loop() {
  // Check if a client has connected
  WiFiClient client = server.available();
  if (!client) {
    return;
  }
  // Wait until the client sends some data
  Serial.println("new client");
  while (!client.available()) {
    delay(1);
  }
  // Read the first line of the request
  String req = client.readStringUntil('\r');
  Serial.println(req);
  client.flush();
  // Match the request
  int val;
  if (req.indexOf("/gpio/0") != -1) {
    val = 0;
  } else if (req.indexOf("/gpio/1") != -1) {
    val = 1;
  } else {
    Serial.println("invalid request");
    client.stop();
    return;
  }
  // Set GPIO2 according to the request
  digitalWrite(2, val);
  client.flush();
  // Prepare the response
  String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n\r\n
\r\nGPIO is now ";
  s += (val) ? "high" : "low";
  s += "
\n";
  // Send the response to the client
  client.print(s);
  delay(1);
  Serial.println("Client disonnected");
  // The client will actually be disconnected
  // when the function returns and 'client' object is detroyed
}