The 7 holidays are literally holidays, like Christmas, thanksgiving, etc, where most everyone is off work.
The 6 days are basically sick days, but you can also use them as one-off "dont feel like working" days .
I would say this is a decent policy by USA standards, but most tech companies have better policies. Amazon pays high salaries to engineers, but the other benefits are pretty poor.
Edit: also, health insurance is optional but most people pay for it. It costs me and my wife about €240 per month, but options range from €45pm to €650pm with my provider. But that is used to cover stuff like queue jumping. I can go to a specialist, get a fast MRI etc, and my private hospital costs are paid. If I didn't have insurance I'd still get that for free, but I'd be waiting for weeks or months to see a specialist. Having said that, some specialists are rare. If you need to see someone who specialises in a particular type of condition you might be waiting a few weeks even if you have the best health insurance imaginable. And when it comes to the big urgent stuff, public health can really work. My sis died from cancer a few years back, and after a 9 month battle, I don't think they paid a cent. She had a lot of life threatening symptoms during the last 5 months and every one of them got immediate care. (That's something I didn't know about cancer - you can wake up one morning with a collapsed lung or a blood clots)
Going to be terse and just say it's not a decent policy in the slightest. Don't be afraid to negotiate for more.
Personally I have never had a white-collar job in the US which started out at 10 days but it does seem to be the average in the US (when starting out) [1]. All of my employers have always started out with 15 days of vacation time with more after a certain amount of tenure. Given the age and experience of OP, I think they are getting shafted with 10 days.
On a side note, the US is truly awful when it comes to vacation and time off from work. The culture here is non-stop work and it's not sustainable.
[1] https://www.cnbc.com/2018/07/05/heres-how-many-paid-vacation...