Tapping on bubbles that appear on your touchscreen will help you select your favorite musical styles. Tap once for "like, twice for "love" and a longpress will make a particular bubble disappear. Repeat with specific artists, and you've given the service enough information to come up with a custom playlist. And the list continues to change as the service adds more information about the music that you're listening to.
You can change your playlist depending on your location and current activity. For example, "Eye of the Tiger" might not be a song you would want to listen to while kicking back after a hard day at the office, but it is a perfect song to motivate you while jogging. The service will cost $10 for access to 20 million tunes when it is launched. This is already a crowded space to begin with, but Beats Music has some deep pockets that should allow it a fighting chance for survival.
Screenshots from Beats Audio on iOS