Usage percentage is a metric that shows how many team possessions you are responsible for ending when you are on the court. It counts field goal attempts, free throw attempts, and turnovers, the three ways a possession can end with a specific player attached to it, as a share of the team's total possessions while that player is on the floor.
There's no such thing as a "good" usage rate. USG% just shows how much of the offense runs through a player, not how well they use those possessions. These bars are typical ranges, not a good-to-bad scale.
Top 5 in the NBA this season, min. 20 games played.
Usage rate doesn't show skill at all. There's no such thing as a good usage rate, it just shows how many team possessions a player uses while on the court.
Not necessarily. High-usage players just take up a lot of team possessions. Whether that usage is efficient or valuable is a completely separate question from how much of it there is.
No. Usage only accounts for field goal attempts, free throw attempts, and turnovers. There are a lot of other ways to add value on the basketball court, like passing, screening, and off-ball movement, that usage doesn't capture at all.