expression, godan verb (-su)
screw up one's courage; take heart
A somewhat literary expression meaning to summon or muster courage, often in the face of difficulty.
彼は勇を鼓して、面接に臨んだ。
He screwed up his courage and went into the interview.
勇を鼓して一歩を踏み出すこと
It is important to take heart and take a step forward.