How do I use this app on my wearable?

When you install the app it should automatically install on the wearable as well. You can then launch it from the list of apps. You can also enable notifications from the app and they will sync to the wearable.

How do I prevent the app from reloading the forecast each time it's opened?

First you want to make sure you are leaving the app using the home button and not the back button. If you use the back button the app will close completely, but with the home button it will only be suspended. You will also need to disable auto updating in the app settings. Press the menu button, select settings, then general. Change the update interval to manual.

What is the difference between the free and paid versions?

The free version displays ads and has a limit of 3 saved locations. The paid version has no ads and no restrictions.