can someone please give me a simple example of code that includes the use of either or both of these functions.
What, the reference isn't good enough? There's a link to highbyte there.
http://arduino.cc/en/Reference/LowByte
Understand that x in lowByte(x) must be a 16 bit integer, type int or word (or other name like unsigned int or uint16_t) and that using unsigned is probably the best when messing with bits.