What is the meaning of Man_up?

To "be a man about it"; to do the things a man is traditionally expected to do, such as taking responsibility for the consequences of one's actions; displaying bravery or toughness in the face of danger, adversity, or a challenge; providing for one's family, etc.

(Of personnel) to assemble, each person manning (attending to) his station, prepared for the departure of an aircraft, ship, etc.

To staff adequately; to staff up; to successfully fill all needed labor positions.

To vigorously guard the opponent to whom one is assigned.

Source: wiktionary.org