There are two built-in light-emitting diodes (LEDs) near the bottom-right corner of the Activity Board WX. They are already electrically connected to Propeller I/O pins P26 and P27.
These LEDs are helpful when developing applications that use sensors. The idea is to build a program that turns on an LED when a sensor is activated. Then you, the roboticist, can get a quick visual cue that the sensor is actually detecting something.