Cindy, go to www.sheldonbrown.com and use his glossary. Look up index shifting there and also read the articles on old bikes, shifting and touring. Bubba says those would all be good info.

Indexing is essentially click shifting pre-integrated brake/shifter days.

First there was friction shifting (ok after Campy invented the derailleur, you wiseacres) - you move a lever and the derailleur moves. By the change in cadence and sound (or looking) you knew to what gear you had moved the derailleurs.

Then, the shifters became "indexed" or click. You move the lever a click and the derailleur moved to the appropriate position . Most modern day bar end shifters (on either drop bars or out on the end of a time trial bar) work this way.

STI shifters combined the indexed shifter lever into the brake levers and we have the "brifter" which is what you use.