OK, sure, we're all making history every minute of every day, some of it memorable and some we hope will soon be forgotten, but with indexing, you make double the history at once: the usual history of your existence and making history accessible to others.
"Huh?" you ask.
Indexing is where you view a digital copy of a genealogical record and type information from the record into a database so there's an electronic index of that record. People searching for their ancestors can then search the indexed records by simply typing in search criteria (such as a name). Without indexing, a person would have to know that their ancestor might have been in some location during some timeframe, get copies of the original records, and manually search through every one of them - which would be extremely slow.
The records which need indexing include all the things you'd usually think of - birth, marriage, death, obituary, and census records - and some you might not have - ship passenger lists, military records, voter registration, and every kind of church record you can imagine. And the records come from all over the world, so you can work in a wide variety of languages.
"But what if I make a mistake?" you ask. It's OK! Everything is indexed by two people and any discrepancies are reviewed by an arbiter. This reduces the risk immensely. And, there are ways to share batches, request help, and just send the batch back so that someone else can work on it instead. So really, there's no stress, just a chance to help make history searchable.
Whether you believe families are meant to be eternal, want to prove you're the rightful heir to some kingdom, really dig your family tree, are curious about people who lived a long time ago, or are simply willing to help others who want to search these records, indexing is an excellent way to kill a little time. It's easy, it's free, and batches are small, so you never need to commit more time than you want. If you're interested, visit FamilySearch.org to sign up as a volunteer (anyone who wishes can do this, no religious or other affiliation or commitment is required).