belgum

train is best or fly

The high-speed Eurostar which brings you within two hours to Brussels, where you change for Gent or Brugge. The trustworthy Man in Seat 61 tells you all.

where di you catch the train from London to go to Brussels and is there a train direct to London from anywhere else in Belgium

All Eurostars start from St Pancras station in London. There is a direct train to Brussels. The trip is a little over 2 hours.
AFAIK it is also the only direct train back to London from Belgium. It's a simple matter to catch another train between Bruges or Ghent and Brussels.

Carrie, you have a lot more research and planning to do. For example, the Eurostar is dynamically priced like an air ticket, and can be very expensive as a walk-up fare. Low prices mean not changeable or refundable. You have to come an hour early for the train for security lines and UK immigration formalities. If there is a Brexit, these may take more than an hour.

Some people buy the Any Belgian Station option to save ticket buying in Brussels, even if it costs a little more than a ticket to Brugge. There are many trains per hour to Brugge from Brussels, unreserved.

The change is at Bruxelles Midi/Zuid, not Centrale, which would be closer to Grand Place, if you hoped to see it.

The actual total travel time is a few hours, and then you need a local city bus in Brugge, to the historic center.