I created an .apk file for the Android version of my app. This apk file is installed on my mobile device, but when I run it nothing happens.

Where can I find a manual to take all appropriate steps to use my app and communicate with the backend on my laptop?

In the app I am currently developing, the background colour of the (body of the) mobile container is set using the properties defined in the theme jqm-Progress, swatch B.
I want this colour to be changed to white.
How can I do that?

Thanks for your clear input

That's great!

Since I need to save only limited data for my proof of concept, I would like to use the easiest option. Is there also written documentation or a tutorial for this option?

I would to like save data locally in the mobile app itself. This data should be available everytime the app is started by the user. Is it possible?