Well, Wiz is right about the 0 zero nic, it means no nicotine.  
Pure nicotine is a white powder.  It tastes very bitter, and a very small amount can be lethal.  But "pure" is rarely found outside of a laboratory, I would never attempt buying(difficult) or mixing my own into a carrier (even MORE difficult), Propylene Glycol (PG) or Vegetable Glycerin (VG).  Most of us rely on buying ejuice with a specific milligram per milliliter ratio.   Sometime we buy a high ratio to mix our own specific strength, I buy 36mg/ml unflavored VG, and the dilute it with plain VG, down to 12mg/ml,  and add my own flavorings.  Makes it much cheaper to use.
 For example if your juice is rated 12mg/ml, that means that there is 12milligrams in every milliliter of your juice. 
That means, 12/1000th's of a gram of nicotine per ml.  That would be considered a mid-strength fluid.  Ejuice is available in many different strengths, be sure to verify density when receiving a new bottle, make sure it's properly marked.
Keep out of reach of kids, pets, and  store in dry cool dark place. 
Most people who use e-cigs do use nicotine, as a cigarette alternative.  Some just want the 'puffing', and possibly flavorings, but 'safer' would be a true statement, 0 Nicotine is safer to use.  But would be a lot like drinking 'decaf' coffee:  I don't know what purpose it would serve.  
Nicotine content doesn't really make a juice 'stronger' tasting, Wiz is right, it's the 'flavoring' of ejuices that give it taste.  Nicotine generally will taste bitter, I understand, so flavorings would mask that aspect and make it pleasant.