Want to understand MySQL indexes?

I have introduced some new people to MySQL recently and had to back track the years to figure out how I learned what I learned about MySQL indexes.  A quick way to get up to speed about MySQL indexes is these three podcasts by Sheeri Cabral.

1. OurSQL Episode 13: The Nitty Gritty of Indexes
2. OurSQL Episode 17: Hashing it out
3. OurSQL Episode 18: De-myth-tifying Indexes

Those three episodes do a good job of explaining how indexes work so that you have a better understanding of how MySQL indexes find your data.