Can't make my app run on an actual device

It was a struggle getting my devices to find each other, and it’s proving to be a nightmare trying to test Xcode apps on a real device. Neither of my devices will accept another upgrade - they both claim to be fully up-to-date (10.11.6 on my MacBook Air and 10.3.1 (14E304) on my iPone 6s Plus) and I’m running the newest version of Xcode (8.2.1). I’ve spent the past 2 days looking for a solution on the internet with no luck - any suggestion?

[edit]this post is obviously too vague to expect precise answers - i apologize…by ‘any suggestions?’, i meant a forum or tutorial on the subject that could help a relative new-commer…

Check out iOS Code Signing: Under The Hood
That tutorial goes over the steps to get your app ready to run on a device.

Have fun!

Thank you for that reference - it’s lessons will greatly help me in the near future…but it doesn’t touch on my current issues. When I enter the error messages I’m given into a search engine, I’m inundated with instructions usually containing steps such as:

“Copy this iOS 10.2 image file to: /Applications/”

Does this sound familiar at all?