Step 1: Click the Start button and select Run( press win key + r ). Now type the following text in that Run box:
notepad c:windowssystem32driversetchosts

You will see a new notepad window on your screen containing some information.

Please read this article before you go for it.
Step 2: Just go to the last line of the file and hit enter and type the following
Save the file and exit. That’s it. None of the above sites will now open on your computer.
You can block as many websites as you like with the above technique. If you want to unblock the website, open the same file as mentioned in Step 1 and delete the above lines.