How to add light switch to electrical wire?

I worked an hour on this yesterday and failed. Maybe someone call tell me what I'm doing wrong?

I have an electrical cord that powers two flood lights on a pole. There is no switch, and I have to unscrew the flood lights to turn them off. I'd like to add a switch to the pole to control the lights.

The electrical cord has 1 black wire and 2 white wires. I cut the cord in half, and tried to figure out which wires to attach to which terminals in the light switch I purchased. The light switch has two terminals on one side, both with gold colored screws, one near the top and one near the bottom. The other side has a single green terminal, very close to the bottom, and lower than the gold terminal on the other side.

I tried attaching 1 incoming white wire to one gold terminal, and 1 outgoing white wire to either the green or the other gold terminal, but it didn't work. I then tried attaching a single white wire and the black wire in various combinations, but that didn't work either.

In all my attempts, there is always a black and a white wire unused and cut in half in the incoming half of the cord, and in the outgoing (i.e., bottom) half of the cord. I think this is where I'm messing up, and that maybe some of those cut cords need to be spliced together to complete a circuit?

Thanks.

Bob