Rotterdam is a lively, vibrant city but, like all places, you need to do some research in advance to get the best from it. Here's the official tourist site: http://www.vvv.rotterdam.nl/uk/
Lovely city.I used to live there. Do explore the markets ,there is usually one most days.The flower market is lovely. The Euromast is a must if you have a stong stomach.A trip to Kinderdyck is also a must. Lots of working windmills.I think they must still do the harbour trip which is is very interesting.
Also you are not far from from the Keukenhof, the beautiful tulip gardens or take a trip to Madorodam a wonderful model village.Shopping is great .
Have a good trip.