"How to say 'be good at' in English?"
You can say "be good at" in English using the verb phrase "be skilled at" or "be proficient in." For example, "I am good at playing soccer" or "She is proficient in playing the piano." Another way to express this is by using adjectives followed by the preposition "at," like "skilled," "proficient," or even "expert." So, "He is a skilled musician" or "They are experts in their field."