Supremely means "as much as it is possible to be." It is an adverb, and it goes in front of an adjective to push that adjective all the way to the top: supremely confident, supremely talented, supremely happy, supremely well organised. It does not just mean "very." It means there is no level above this one. If you say a singer is supremely gifted, you are saying you cannot imagine a more gifted singer.

Because of that, it sits mostly with adjectives that describe good or impressive qualities — confident, capable, skilled, beautiful, elegant. You will hear "supremely confident" all the time in sports writing. It can go with a bad quality too, and then it sounds a little dry or joking: "He was supremely unhelpful." That is a teacher or a journalist being clever, not everyday speech.

One more thing, and this is the part students miss: the word feels written, not spoken. It belongs in newspapers, book reviews, and formal praise. In ordinary conversation a Taiwanese student's friends would say "really confident" or "so confident." If you say "supremely confident" in a casual chat, people will understand you perfectly, but they may hear you as sounding bookish. That is not wrong — it is just information about the room you are in.

There is also a smaller, older use where it keeps its link to "supreme" as in "highest in rank," as in a ruler who governs supremely. You will meet this only in old or legal writing; it is not the meaning you need first.