You should have really told us some more details about your configuration (ip addresses, ...) - how can you expect help with a problem without giving some more details about it?
Without knowing anything about the config in more detail I'd also think that you probably use private ip address space for your "workstations" and don't have a src-nat rule in place. You should read up in the manual about this, but a quick shot would be something like
/ip firewall src-nat add src-address=<your internal network address like 192.168.0.0/24> out-interface=<your interface to the internet, like ether1> action=masquerade
.
If this doesn't help, please come back with some more details...