Installing Layouts Tips (Android)

Usually when people download a .acronrpn file with Chrome, they can just use Open from within Chrome and it will apply the layout automatically.  If it is opening in some other app, it's because that app has set itself up as the default for all XML files. 
If you're using some other browser, I'd recommend trying it in Chrome.  I've had problems with other browsers not honoring the OS's MIME type mapping.
Alternatively, you can use "Open..." on "Pg 2/2" of the "stack" toolbar.  If you downloaded it in Chrome, the file should be available via "Downloads" in the Open From.  Or you can save it to Google Drive - that's also an option for where you can open from.
Also, Acron RPN is set up to receive shared .acronrpn files.  So, for instance, you can share from a gmail attachment or Google Drive and Acron RPN will be one of the options of what to share to.