what is the brand?
either way "play music" app by google should be pre-installed, play music you put on your phone from that.
also go to settings > security, and check unknown sources. this let's you install apps from the Internet for free.
http://m.android-4-4.apps.opera.com...ea93_70572753/tubemate_youtube_downloader.apk
^ tubemate lets you download youtube vids or just the audio and actually save it in your library as well.
then say you find an app you want on play store but it costs money google its name followed by apk. and it will likely give you links to blogs with links to download these apps.
to make things a lil clearer .apk = android package. it is the file type for an android app that needs to be installed.