Need help converting a 240V outlet to a 120V outlet

I bought this house and I am guessing the former owner had something
outside that ran on 240V. All they left were a bunch of wires hanging
out of the wall. I want to make it into a regular 120V outlet.
The breaker is a dual 30Amp breaker with a white wire and a black wire
coming in.
Picture here: (The breaker is switched off)
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There are two sets of 3 wires coming out of the wall. They both have a
black wire, white wire and bare wire.
Picture here:
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The smaller set does not seem to show any voltage at all.
Is it easy to make this into a 120V outlet?
I was hoping all I would have to do is remove the metal clip that binds
the circuit breakers together and flip only one and I would get 120V,
but that is not the case. It goes to zero when I do that.
I read some on the net and maybe I need to move the white wire from the
breaker to the neutral pole in the breaker box?
Any help is appreciated.