On Thursday, July 21, 2016 at 8:08:45 PM UTC-4, wrote:
On Thu, 21 Jul 2016 10:03:58 -0700 (PDT), Davej
wrote:

On Wednesday, July 20, 2016 at 5:02:28 PM UTC-5, wrote:
a while back I removed a backyard pond. I connected the old
wiring from pond to my shed. Three 10 ga wires - black, white
and green. I picked up a 30 amp breaker box from Menards and
it has room for two 15 amp circuit breakers.

You don't explain where this wire is coming from or how long it
is. It should come from a 15a or 20a breaker on the main panel.

Black is hot. White is neutral. Green is earth ground. That is
the standard color code but you can't trust that is true until
you verify it. A 10 gauge wire at 120V should go through a 15a or
20a breaker. If the wire is long then a 15a breaker may be best.
The black (Hot) wire goes to the breaker. The box may accept two
breakers but you can only use one breaker. Turn off the power
before messing with it. Contact an electrician if you are uncertain.
Use a test light to verify that black is indeed the only hot wire.
Since it is not going to be 100% to code anyway,

Who decided that?