The darlington configuration is two transistors connected in
such a way that the gain (hFe) of the pair is higher than either
transistor taken individually. The two collectors are connected
together, and used as the collector of the pair. The base of the
first transistor is the base of the pair. The emitter of the first
transistor is connected to the base of the second transistor. The
emitter of the second transistor is the emitter of the pair.
Sometimes there is a resistor between the second base and the
second emitter, so as to stabilize the pair in certain conditions.
Typically, you multiply hFe's in darlington configuration, so if
each transistor had an hFe of, say, 100, then the hFe of the pair
would be 10,000.