Intersection of each axis is the league average for those that have played more than 120 minutes(~55% for True Shooting and 19.2 for usage). The “S”s you see are the team average for each team for True Shooting. Only players with >120 minutes played this season are included in the game primer.
A reflection: Luka often has the highest usage in the league, so plots including him can get a bit awkward.
Data from Basketball Reference.