With the iPhone 6s, you have the ability to set up a fingerprint for unlocking your device and also for using Apple Pay. This support document explains setting up Touch ID with your fingerprint. You can set up multiple fingerprints. Use Touch ID on iPhone and iPad - Apple Support I cannot find any information about using your passcode for Apple Pay. You can see this Support document for information about setting up Apple Pay. Set up Apple Pay on your iPhone, iPad, or Apple Watch - Apple Support
As far as the boarding pass, you will get information in an email from Delta, and it will contain information about adding the pass to your Wallet. You can also get the Delta app in the App Store and obtain information from that. I have used this with Delta on multiple occasions, and it works great. You just display the pass on the screen and lay it on the reader. Quite nice.
Apple Fingerprint Setup
San Francisco: The US Patent And Trademark Office has published a new patent application from Apple which reveals that the company is working on a new watch that will make the wearable more useful to the user through the addition of the Touch ID fingerprint scanner support, news portal GizmoChina reported on Friday. Touch ID is the one that might affect your day-to-day Apple Watch use the most. Top ten drawing software. “The display may also provide an input surface for one or more input devices, such as, for example, a touch sensing.