Your first circuit

A simple steady-current circuit needs a complete conducting loop. Conventional current leaves the battery’s positive terminal and returns to its negative terminal through the external circuit. Electrons in metal move in the opposite direction. Opening this single-path loop stops its steady current.

Compare it to a model train track. The train (current) only keeps rolling if the loop of track is complete. Lift out a single piece of track and the train stops — it has nowhere to go. A circuit is identical: electrons need a continuous path all the way back to where they started.

An LED conducts readily in the forward direction and normally stays dark in reverse. On many through-hole LEDs the longer lead is the anode and the shorter lead is the cathode; confirm the actual part’s markings. Excessive reverse voltage can damage an LED, so backwards connection is not always harmless.