In reply to Heike:
If it's anything like the Forerunner 735XT that I bought recently, the manual is not really very helpful (having downloaded the manual for the Instinct: yes, it looks very similar in style i.e. densely written, neither structured so as to communicate the basic principles of the device well, nor particularly easy to use as a reference.) The style of these manuals strikes me as being characteristic of user documentation written by someone who knows how the thing works and can't get themselves in to the head of someone starting with an effectively empty knowledge base, and minimal context within which to comprehend the words in front of them. It's not helped, of course, by the fact that so much tech these days is supposed to be so easy and obvious to use that it doesn't need a manual. Yeah, like heck.
I found that the best way to get the hang of my Forerunner was just to play with it for a while - even pressing buttons randomly to see what they do in different contexts or on different menus. If you manage to mess up the settings you should be able to reset it back to the factory settings and start again:
https://www8.garmin.com/manuals/webhelp/instinct/EN-GB/GUID-46551446-AAE7-4...
and if it hangs, just restart it:
https://www8.garmin.com/manuals/webhelp/instinct/EN-GB/GUID-626CD309-6FCC-4...
Fairly obviously, you need to do this before you plan to use it in anger!
I surprised myself by managing to work out how to install an app from the Garmin store on to my Forerunner that gives me a 10-figure OS grid positional fix. That felt good, having initially been disappointed to find that it didn't do it "out of the box".
Good luck!