It depends on where you want to go.
Go to Saint-Lazare Station, take RER E, the first stop is Gare du Nord station the one where Eurostar are leaving from to London
You would need to go to Liverpool Street station to travel to Stowmarket.
London Paddington.
Not directly, you have to go to the train station in London Paddington and take a connection train from there.
Take a train from London Waterloo station.
Kings Cross
Take a train from Ipswich to London Liverpool Street. At Liverpool Street, go to the tube station and take a westbound Circle/Met/H&C Line train to Paddington. At Paddington, go into the mainline station and take a westbound train that stops at Slough (it should be the first station the train calls at). From Slough, take the shuttle train to Windsor Central. At Windsor Central, leave the station and follow the signs to Riverside station, the other railway station in Windsor. At Riverside station, you can catch a bus to Legoland. Don't miss Windsor, by the way.
Bedford is approximately 80km north of London. To travel by train you would need to go to St Pancras station in London or by car take the M1 or A1 from London and follow the signs.
Take a train from Paddington Station
30 minutes if there are no issues in the London station
St.Pancras
Liverpool Street.