"The only stupid question is the one
that goes unasked."
^ Seriously. Remember that.
If you've been in academics for 6 years, I'm assuming (and hoping) that you have a solid grasp on core engineering concepts. Unless you've gotten yourself in a bad situation with a terrible employer, they should be aware that being fresh out of school in your first job, you'll have a learning curve ahead of you and be expecting you to make mistakes along the way.
If your skills didn't match what the employer was looking for, they wouldn't have hired you. If they hired you even though your skills don't match what they're looking for, then you most likely don't want to work there anyway.
The more questions you ask, the faster you will become accustomed to your new work environment. Having said that, generally engineers don't like constantly being bugged as it takes ~15 minutes for them to get back in the swing of things. So, I'd maybe think about putting all of your relevant questions in an e-mail and sending them to someone in "the know" at the end of the day.
Some companies pair you up with a mentor, some don't.