This is the 85th most frequent Japanese word.
どう
"How" or "in what way."
In this instance, "どう" is used to ask for an evaluation or impression of the dish.
この料理はどうでしたか？
How was this dish?
In this sentence, "どうやって" means "how," and it is used to inquire about the method of performing an action.
それはどうやって使うの？
How do you use it?
Here, "どう" signifies "what kind of," referring to forming an opinion.