This idiom means pretending to have skills one does not possess.
Qí Xuānwáng xǐhuan tīng chuī yú érqiě yào sānbǎi rén yìqǐ chuī
齐宣王Qí Xuānwáng🔊喜欢xǐhuan🔊听tīng🔊吹竽chuī yú🔊，而且érqiě🔊要yào🔊三百人sānbǎi rén🔊一起yìqǐ🔊吹chuī🔊。
Nánguō xiānshēng gēnběn bú huì chuī yú què hùn zài yuèduì lǐ zhuāngmúzuòyàng
南郭先生Nánguō xiānshēng🔊根本gēnběn🔊不会bú huì🔊吹竽chuī yú🔊，却què🔊混在hùn zài🔊乐队yuèduì🔊里lǐ🔊装模作样zhuāngmúzuòyàng🔊。
Qí Mǐnwáng jìwèi hòu yào měi gè rén dāndú chuī yú
齐湣王Qí Mǐnwáng🔊继位后jìwèi hòu🔊，要yào🔊每个人měi gè rén🔊单独dāndú🔊吹竽chuī yú🔊。
Nánguō xiānshēng zhǐhǎo tōutōu táozǒu le
南郭先生Nánguō xiānshēng🔊只好zhǐhǎo🔊偷偷tōutōu🔊逃走了táozǒu le🔊。
English Translation:
King Xuan of Qi liked listening to the yu being played, and wanted three hundred people to play together. Mr. Nanguo could not play the yu at all, but hid in the orchestra pretending. After King Min of Qi succeeded to the throne, he wanted each person to play the yu alone. Mr. Nanguo had to flee secretly.