How can I unblock sites blocked in my country? such as facebook

You can use proxy server to access the blocked websites
List Of prime Free Proxy sites : if you are using chrome

Gom vpn (https://chrome.google.com/webstore/detail/gom-vpn-bypass-and-unbloc/ckiahbcmlmkpfiijecbpflfahoimklke?utm_source=chrome-ntp-icon)


Unblock Proxy Free Vpn | Hotspot Shield (https://chrome.google.com/webstore/detail/unblock-proxy-free-vpn-ho/nlbejmccbhkncgokjcmghpfloaajcffj?utm_source=chrome-ntp-icon)


Browsec (https://chrome.google.com/webstore/detail/browsec/omghfjlpggmjjaagoclmmobgdodcjboh?utm_source=chrome-ntp-icon)


Zenmate Security Private and unlock vpn (https://chrome.google.com/webstore/detail/zenmate-security-privacy/fdcgdnkidjaadafnichfpabhfomcebme?utm_source=chrome-ntp-icon)

These are the best Vpn so far, it doesn't matter how tight the security check is.
Any one of them will help you easily bypass that check.

Good Luck.!
Happy Browsing.