I'm studying Chinese. If I run across a sentence whose grammar I can't parse, I paste it in and say, "Can you explain this sentence?" It will usually break it down, phrase by phrase, explaining what each thing means and how it fits within the whole. If it doesn't, you can ask "Can you break it down in more detail?" If there's a specific word you don't understand, you can say "What is the word X doing in this sentence?"

You have to watch it, because it does hallucinate (at least, GPT-3.5; I'm using the API and haven't been given access to GPT-4 yet). In one instance, it said that a series of characters meant X in Chinese, when in fact I happened to know it was just a transliteration of a different language, and not in Chinese at all. But it's still helpful enough to be worth using.

You can also ask it to give you example sentences with a specific word; and I've had some success asking it to generate sentences in which then word is used in the same way, or with the same grammar structure.