“I had chocolate cake for dessert, which was good but nothing special.”
You went out to eat at a restaurant, and now you're writing a review of your meal on a restaurant-review website. You write this about a piece of cake that you ate, which wasn't very bad or very good.
I had chocolate cake for dessert, which was good but nothing special.
You can use the word "have" to describe eating something:
We had Italian food. What are you having?
Use this pattern to combine two ideas. For the example at top, the two ideas are:
I had a chocolate cake for dessert. The chocolate cake was good but nothing special.
Here are a few more examples of how you can use "which":
We're planning a trip to Australia, which we've never been to. Eric's mother is coming to visit us, which is great. It was less than $100 for the four of us, which is quite reasonable.
The phrase "nothing special" describes something that is not bad, but not particularly good either. Use this when you wanted or expected something to be good, but it wasn't.