If you have never downloaded an app outside of the Google Play Store, you will have to allow application installation from other sources. To do this go to:
Settings -> Application -> Unknown sources
Settings -> Security -> Unknown sources
The Lite version contains only the Zions Harp, Junior Hymnal, Gospel Hymns, and the Hymns of Zion. It is 130Mb.
The full version contains the entire Lite version of the app, as well as several versions of the Zbirka and the Pisne Chorale. It is 230Mb.