NXT light sensor homework help
Without solving your homework, you will need at least the following blocks:

for bullet 1


Light Sensor
Data to Text
LCD Panel Display


for bullets 2 and 3


Loop (forever)
Switch (based on light sensor readings)
Motor Block (4 of these, 2 for > 50% + 2 for &lt;= 50%)


And it probably makes sense to put bullet 1 inside the loop of bullets 2 and 3.