nǎn is literary — you will meet it mainly in formal writing, classical-style essays, and polite self-deprecation. Modern spoken Chinese uses
脸红 (to blush) or
不好意思 (embarrassed) instead. Common compounds:
赧然 (blushing — adverbial),
赧颜 (literally 'red face', a polite phrase for shame),
羞赧 (bashful, shy).