Talking about how to unblock websites previously, then how to block any websites?
If you want to block any websites from your computer either for children safety or for blocking any software websites for running sudden automatic updates, then you can do it directly from your PC. Actually, there are many websites and free software on the Internet that can offer you the best solution to block any websites but sometimes you just need to worry about a software installed which has the potential to infect your system and are absolutely irritating.

But if you don’t want to become those malwares’ target, then I would suggest you to try out a free and easy way to block websites without using any software.

First, go to the directory of your PC where the Windows was installed as below:
C:\Windows\System32\drivers\etc

Then, find for the file with a name “hosts”.
Open that file using any text editors.

To block a website, add this line of message
127.0.0.1 website1
after the following two lines of message as shown below:

To block more sites, just repeat to add,
127.0.0.1 website1
127.0.0.1 website2
and so on, just like the screenshoot below.

Replace website1 with a website www that you want to block, same for the rest.
Go back to your browser and visit back the sites that you have blocked. Done!

To unblock any websites that you have blocked, undo all the steps you’ve done.