How do I use Passbook and is it safe?

Check this link.

http://support.apple.com/kb/HT5483?viewlocale=en_US&locale=en_US

I use it mostly with Airline boarding passes, and with a Walgreens reward's card. Not sure how much safer using it can be with my boarding pass scanned before entering the plane and my Walgreens card scanned when making a purchase and when redeeming rewards.

Start here for instructions on use:

http://support.apple.com/kb/HT5483

I'm not sure what you mean about safety. It's no less safe than carrying around paper versions of things. You do have a passcode on your phone, right?

Best of luck.

Yes, Passbook is as safe as any app of this kind. To keep a high level of safety turn on Passcode lock and use it. Also make sure you have Find My IPhone turned on.

I use Passbook to store my Amtrak Tickets and airline boarding passes when I travel. There are many other uses though such as storing store coupons, movie tickets, etc.