Ships dock near the Erasmus bridge in Rotterdam https://www.cruiseportrotterdam.nl/directions/
Rotterdam itself is a nice place to visit with a lot of modern architecture (for example cube houses), bridges, the Euromast, the Market hall, lots of musea, etc.
Gouda is very different from Rotterdam, smaller, but also a nice place to visit. It has a very nice market area with many old buildings. The actual cheese market is only in summer (and very touristy). More info about Gouda can be found at https://welcometogouda.com/
Apart from cheese Gouda has also given its name to 'Goudse Stroofwafels' (sirop wafels). Be sure to buy some when in the Netherlands (any supermarket sells them, but the freshly prepared ones at special bakeries are of course nicer and usually bigger).