Hi Vix67
The visitors centre is opposite the Roman Coliseum, just a few minutes from the city centre (where all the shops are anyway). Follow the road past the coliseum and turn right into St John Street (you'll see the "Off the Wall" pub on the corner). You can see WH Smith right ahead; then you're in the centre.
You'll see the City clock - follow the road to the end until you get to the subway. In the subway, head towards City Road, at the end of which is the train station.
The train station is a bit further away, probably a good ten minutes to walk, but easy to get to. There are lots of hotels on City Road at pretty reasonable prices.
Hope this helps.