There are so many threads of newcomers asking this question. Hopefully this thread can answer everyone's questions.
THIS IS ALL YOU HAVE TO DO TO INSTALL AND PLAY THE GAME.
STEP #1:
Go to this website and download the PlanetSide Launchpad. To do this go to the bottom and hit "reinstall" next to PlanetSide. No purchase required!
http://www.soe.com/getthegame/?locale=en_US
STEP #2:
Head to the SOE Game Pass page and select PlanetSide. Hit "Get your Pass" and proceed through the subscription process.
http://www.soe.com/gamepass/?locale=en_US
STEP #3:
Open your PlanetSide launchpad, log in, and wait for the game to patch. Press the big "PLAY" button.
That's it. You've successfully managed to download and subscribe to PlanetSide. Enjoy yourself!