Some routers you can feed them custom DNS servers and then any device that connects to them will use those settings, otherwise you'd need to change them on a device-by-device basis.
Google provides a DNS service (as above, considering it provides everything else these days
) but the alternatives are OpenDNS and Level 3. List here:
A DNS server to put it very simply is a conversion process to make the internet human friendly. Without it instead of going to google.co.uk we'd have to go to 22.214.171.124 instead. So basically if you can't get on tvforum.uk
from one connection that means your provider has an out of date entry for the website so it's looking in the wrong place. These issues usually resolve themselves within 24hrs.