First of all you'll need the rc-switch library (thanks to sui77 for this library and example code). You can get this from https://github.com/sui77/rc-switch

Once you have this installed you can simply load the example called ReceiveDemo_Advanced. With this example uploaded to your ESP8266 you should be able to 'sniff' the 433mhz signals from the transmitter that came with your remote socket.

Open up the serial monitor in the Arduino IDE and press a button which switched on the socket on your remote that came with your remote socket, and you should see something like this:

Received 1394007 / 24bit Protocol: 1

These are the only real import parts that you need to keep an eye out for, and you'll need to put these into the sending script to send the same data to the remote socket to switch on.

Then do the same for the off button on the remote, again make a note of the code.

This library and receiver supports the following chipsets: