In the Warring States Period, the State of Qin besieged the capital of the State of Zhao. Duke Pingyuan of Zhao planned to ask the ruler of the State of Chu personally for assistance. He wanted to select a capable man to go with him. A man called Mao Sui volunteered. When the negoti-actions between the two states were stalled because the ruler of Chu hesitated to send troops, Mao Sui approached him, brandishing a sword. At that, the ruler of Chu agreed to help Zhao, against Qin.
战国时代，秦国军队攻打赵国的都城。赵国的平原君打算亲自到楚国去请救兵，想挑选一个精明能干的人一同前去。有一个名叫毛遂的人，自告奋勇愿意同去。平原君到楚国后，与楚王谈了半天，没有一点结果。毛遂怒气冲冲地拿着宝剑，逼近楚王，终于迫使楚王答应出兵，与赵国联合共同抵抗秦国。
This idiom means to recommend oneself.
“毛遂自荐”这个成语用来比喻自己推荐自己，不必别人介绍。