tov% = turnovers divided by possessions.
Possessions, in case you don't know, are determined by the following: (FGA + TOV + (0.44 * FTA)).
As for how their usages can be similar and top48 with different tov%... Turnovers count as a possession, which counts in usage. You can have the same number of possessions per minute, but a different distribution of those possessions. Does that make sense? They also played different minutes in different eras (pace issue, which is what usage is supposed to balance).
According to WIS, they use tov% to determine whether a player turns the ball over or does something else to end the possession (shoot a field goal, get fouled). Why they don't tell us what each player's tov% is, I have no idea. You have to go to somewhere else for players post 1977-1978, and before that, you have to do math.
It's the number one thing I've been asking for from WIS for almost a year. Show me tov%, and allow me to search for it and sort by it in the draft center.