It’s super simple: the installation file, AutoIndex.sql, creates an Agent job and a series of stored procedures including auto_create_index and auto_drop_index. They watch the index usage and missing index DMVs, log their findings to tables, and trend the data over time in order to figure out which indexes to create, and which ones to prune back because they’re only slowing you down.
And it’s even free!
I enjoy these posts, where Brent goes back to ideas people had 20+ years ago. It really shows how creative the SQL Server development team was back in the day.