Outstanding, easy to use app. Via a built in browser you can search the usual music sources but the easiest way is to find a song on YouTube using the shark fin button. Use YouTube search, touch the share symbol (<) under the video frame then press its blue YouTube link for the copy command. Link copied you then go to the "mp3 Tube" button, paste the link into the URL field and with the press of a conversion bar then a download bar the app holds the song for you for offline play. You are limited only by your devices memory. Plug your device from its headphone jack into your car stereos aux in jack with a simple double male ended stereo cord (look for 2 little black bands on the prong instead of 1) adjust your stereos sound and volume, and youre ready to roll. (USB-in may work but there is support and latest stereo firmware issues to consider.)
On an 16 gb iPhone 5 the procedure only took seconds for each stage. If you experience slow search and download times try closing that multitude of apps that are on in your devices background. :)
Apps of this nature often have limited lifespans so be grateful and enjoy it while you can. Back up your device with your songs in the app for possible later enjoyment should the app go bye bye from the app store.