super su needs to be flashed from recovery in 5.0 , flash a custom recovery like philz or TWRP, get the supersu zip from xda it is there on s4 forum , flash it from recovery.
Yes, exactly. That's the most wise way to install SuperSU. Get the zip, the latest version is 2.46, and flash it in recovery, be it TWRP or whichever you prefer. No need to install any app from Play, SU will be automatically installed.