The Indexer can be used in a variety of ways, but the main intent is to place it between two fingers (usually index and middle). This typically places it further forward on the handguard, which also means it doesn't get in the way when transitioning to kneeling or prone shooting positions, where most people move their support hand towards the rear. Used in this manner, the Indexer makes it much easier to pull the rifle into your shoulder and maintain control while shooting.
