If you're a totally new player, you can buy the standard version or the Collector's Edition "Infinity" and both include 'vanilla' Rift, so yes, you get the original game plus expansion
If you already have original Rift, you can just get Storm Legion alone, however i think that'll be Digital Download only, i don't think you'll be able to buy the Expansion alone in shops...i might be wrong
http://stormlegion.riftgame.com/en/preorder/