Identifying and correctly using this component
Putting a photodiode and a LED in series won't do anything useful.  Photodiodes work on much lower currents than LEDs do.

There are two ways to use a photodiode, in forward mode like a solar cell, and in reverse mode where the light causes leakage.  Generally the second method is simpler because the current is directly proportional to the light level (of the wavelength of light that the photodiode can see).

Try this:



Q1 and Q2 amplify the tiny leakage current from photodiode D1 to eventually drive the LED D2 to about 10 mA.  The LED will light with very little current into the base of Q1.  Putting 1 finger on the 5 V supply and the other on the base of Q1 should easily light the LED.  To decrease the sensitivity, make R1 smaller.