Jackinthegreen
Explorer
When I read that feat, I see it saying that you get one attack per round with that off hand weapon. So, by my reading the 6th level Ranger with a BAB of +6 gets a total of three attacks per round: Full BAB (adjusted for two weapon fighting) with both primary and secondary weapons, and a single iterative attack with the primary.
If you want extra attacks with that second weapon you need Greater Two Weapon Fighting.
At least that's the way I read it. I've been wrong before.
The mechanics part is correct. A BAB 6 character with TWF would have an attack routine of +6/+6/+1, or when adjusting for TWF's best penalties it's really +4/+4/-1 based purely on BAB.
You're a bit off on the feat name though. Improved TWF is what grants the second off-hand hit, and then Greater TWF allows for the third.