As everyone else has confirmed, the word here is 'make'. Preparing and putting together ingredients for a cold dish does not count as 'cooking': we make salad. Also note that this holds true even if the salad contains cooked ingredients, such as many Russian salads. First you might cook potatoes, beans, chicken, or whatever else you need, and then, finally, you 'make the salad'. This means that you assemble the components.
Another thing to note: The dictionary definition <em>To prepare (food) for eating by applying heat </em>is actually a little misleading. The key word here is (solid) food, rather than just the idea of heat. Here's why:
We don't use 'cook' for soups, despite the fact that heat is involved. We make soup, even though the ingredients of the soup need to be cooked. For example, you might say "I'm making borscht. It's not ready, though. The beets aren't cooked yet".
We definitely don't 'cook' hot drinks. We make tea and we make coffee, or more rarely, 'brew' these drinks.
Also note that we don't usually 'cook' things that involve dry heat in the oven, especially if they are sweet: in these cases, we use 'bake'. For example, we bake cakes and we bake pies. As with the soup and salad example, the individual components need to be cooked, but we bake the dish itself.
And how about savoury dishes cooked with dry heat in the oven: pizza, for example. Well, in those cases, we generally use the all-purpose verb 'make': we usually make pizza.
Handy tip : if in doubt, use make.
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One final point: English speakers never write <em>smth.</em>
99% of English speakers are confused by this strange sequence of four letters and assume it's mistake. Meanwhile, those of us who are used to seeing this Russian habit are curiously irritated by it. Please don't do it! Just write the full word: something.