The Crowbar is a melee weapon. Like the Hatchet it is normally put into your toolbelt but can be taken out to replace your main weapon if any by Right Clicking and selecting, "Remove from tool belt." If you have a Main Weapon in hand when you do this it will drop that weapon. 

Unlike the Hatchet it takes several hits from a Crowbar to kill a Zombie, this is changed in DayZ 1.7.7 but is still true in Breaking Point at this time. As a New Spawn this is better than not having a weapon. It is a quiet way to kill zombies but because it takes several hits to kill them it gives the zombies more time to hit you back and so it not recommended if you find anything better.  The most likely place to find a Crowbar is in Residential loot piles.