How to integrate a third party app ?

Hi
I am wondering how to integrate a thrid party app ? 

Let's say "MyApp" has some fields like "remaining activity time" , "an energy level" , "an award level" that are displayed in a smartphone app. 
The use of this app is trending together with people using garmin watches. 
Instead of handling their smartphone during a run the idea would be to cast this "MyApp" onto the watch screen. 

Who would feel like able to do this ? 
I am super eager to learn the main steps for this and being collaborative. 
This can (will (I hope) ) lead to the development of a connectIQ app ;) 

Cheers,
Max