How can i block website or ip from my mikrotik router?

I need to stop my staff from accessing Facebook and Twitter during working hours, how can i control it from my mikrotik router board 750?

Thank You

Have you searched the forum? It's discussed so many times...

I tried this but its not working. Does it matter what position the firewall rule is? Right now its at the end.

Can anyone tell me why this isn't working?

I tried this but its not working. Does it matter what position the firewall rule is? Right now its at the end.

Move that rule to top and will start working!