Can you block websites like Facebook with Avast Endpoint not the suite or suite plus product?
You should use the options the server OS is giving you to block websites.
short answer: Yes you can block those sites via de Avast client.
Long answer: Yes you can still block that but if you need more control over what to block and who is accessing things you should look into a better solution. Barracuda or watchguard or Juniper or Cisco have that kind of filtering appliances