I have a Samsung S7 Edge. My wife has an Apple I6. Is there a way or an app that we can use that updates a common calendar? In other words, when either of us puts in a calendar entry, it would update the calendar on the others device.
Yup, Google Calendar! You'd need to use a shared Google account or share your calendar with hers (and viceversa), however. There are other apps/services that would let you do this with independent accounts, but I haven't use them so can't recommend them or couldn't be sure that it would work cross-platform.