What is this on power supply unit?
Disclaimer: If you don't know what you're working with, I suggest you hire someone to help. I know it's not what you want to hear but it's better safe than injured or dead. You only get once, maybe twice to seriously mess up.

From left to right on the back:

The AC "L" and "N" probably mean "Live" and "Neutral" respectively. The ground next to it is the Earth ground. The V+ and COM are the DC output terminals, which you could also say are V+ and V-, respectively.

Just some clarification: What you're referring to when you say V- is probably "ground" or to be precise, 0 Volts. With respect to the circuit with the LED anyways. COM and V- and Ground can all mean 0 Volts. However, V- is typically reserved for actually negative voltages, like -10V, etc.

The reason why there is a set of two is probably because there are two "rails." A rail acts as an independent supply so that you can easily isolate or distrubute loads so that two separate circuits don't interfere with each other or rob each other of too much power. This is just a guess since there's zero documentation for this supply. Also without documentation we don't know if it's possible to run those outputs in such a manner you can power the one 180W LED without some other external circuitry.

A lot of high power LED's I've seen run at ~30V or so. Power = Current x Voltage, so 180W = Current x 30V, solved: 6A of current. You'd set the output voltage of the power supply by using the adjust potentiometer "+V ADJ" before connecting anything.

According to the following table you probably need 12 gauge or larger wire (allowing more amperage to over-rate so the wires don't heat up easily).

http://www.powerstream.com/Wire_Size.htm

Also another consideration: Be sure the LED has plenty of heat sinking otherwise it will burn up immediately. Even 20W - 50W LED's can require heatsinks as large as a typical desktop CPU's (including a fan).