Hello. I am powering a 250 watt metal halide lamp how much amps will it use or do I need

Look up Ohms law and you will get your answer

Ohm's law is stated as follows:
P=IxE
P is power Or watts
I is current or amps
E is applied voltage
In your situation, assuming that you are using 120 volts, the answer to your question is as follows:
P (250)= I(x for unknown amps)x E (120 volts)

250=120x
x=250 divided by120
x=2.08333333 amps