Replaced ceiling fan with a light fixture. Each set of wires had 1 black, 1 neutral, 1 ground. The fan was wired as follows. Two black and the neutral from the hot black together, 2 neutral together, and the wires from the fan were all connected to the remaining hot black. After I removed the fan, I connected the light as follows: I removed the 1 neutral that was previously connected to the 2 black and attached it to the white from the light. I recapped the 2 black together. I left the other 2 neutral as they previously were. I connected the hot black to the black from the light. I then replaced the wall dimmer switch with a singe toggle (on/off) switch. When I turned the circuit breaker back on, the light was on, but I could no turn it off at the switch. Also, the light in the next room would not come on.

How should they be wired? Thank you, Phil Harris (Oklahoma Grandpa)

The white wire that you saw connected to the "Black" supply was a re-tasked wire and should have had a band of black tape or been colored black. Although the wire itself is white, it is not being used as a Neutral. It is being used as a hot feed to the switch.

This is a switch loop. You connect the feed to the wall switch (White) is connected to the "Supply Black". The return back from the switch (Black) would then be connected to the "Black" on the light fixture.