"Hello World" program for nRF24L01+?
Here are several "getting started" articles that contain simple programs.

http://tmrh20.github.io/RF24

https://groups.google.com/forum/#!topic/nrf24-arduino/VaC2U5D1o_s

http://arduino-for-beginners.blogspot.com/2013/02/setup-nordic-nrf24l01-rf-modules-to.html