Single player is very fun and most recommended for the very beginners.  But, completing the single player is completely unnecessary, for it doesn't begin to prepare you for the EXTRAORDINARY online gaming experience.  Although playing online is free, I would GLADLY pay the price of this game as a monthly fee if need be!  A little about the game.. you start off with a single building for your base.  As the game progresses you build yourself a bigger base and, depending on the game type(which there are plenty of), you make forces to attack and defend.  Too much fun to be able to explain why!